Which mathematicians have influenced you the most? There are mathematicians whose creativity, insight and taste have the power of driving anyone into a world of beautiful ideas, which can inspire the desire, even the need for doing mathematics, or can make one to confront some kind of problems, dedicate his life to a branch of math, or choose an specific research topic.
I think that this kind of force must not be underestimated; on the contrary, we have the duty to take advantage of it in order to improve the mathematical education of those who may come after us, using the work of those gifted mathematicians (and even their own words) to inspire them as they inspired ourselves.
So, I'm interested on knowing who (the mathematician), when (in which moment of your career), where (which specific work) and why this person had an impact on your way of looking at math. Like this, we will have an statistic about which mathematicians are more akin to appeal to our students at any moment of their development. Please, keep one mathematician for post, so that votes are really representative.
 A: Thurston.  When I was a graduate student, Thurston's work really inspired me to appreciate the role of imagination and visualization in geometry/topology.
A prominent mathematician once remarked to me that Thurston was the most underappreciated mathematician alive today.  When I pointed out that Thurston had a Fields medal and innumerable other accolades, he replied that this was not incompatible with his thesis.
A: Joseph-Louis Lagrange For his modesty as a human being, and his great mathematical work, on almost every field of mathematics, but especially in mechanics.
A: Gromov.

A: Terence Tao. He is one of many who influenced me the most. I don't have to mention how superb his blog and publications are. From his writings I found analysis of PDE as a fascinating subject and I am really happy that I found this topic not too late. It amazes me how much he produces.
A: Andrew Gleason. An inspiring teacher in Math 55, the 2nd-year advanced calculus course at Harvard, and Math 213, the graduate complex variables course. He had a knack for getting at the essence of anything he lectured about. I have tried (with considerably less success) to do that in my teaching and my writing. 
A: I have quite a few on my list. 
Newton and Leibniz since the day I learned they were 22/19 (respectively) when they invented the calculus, Riemann as well (one of my teaching assistants was mad about him as well... it caught on)
Gödel after I'd took a course focusing on completeness and incompleteness, as well after you read his biographies.
Saharon Shelah, after one of my professors that did his Ph.D. under Shelah told me a lot about him. Finished his master degree in one year, Ph.D. in two. Invented so much... he's a real inspiration for me.
Grothendieck is a personal inspiration from another end. Not as a mathematician but as a human being. The fact he was able to get up and leave everything. That is amazing for me.
And while we're at it, Albert Einstein since I was 21 and read the book Ideas and Opinions.
What matters is less the work, but rather the ability to express with clarity a new idea that no one had before. That's what makes a great mathematician in my eyes... at least from where I stand today.
A: Curtis McMullen. If you have ever seen him give a talk, you'll know what I'm talking about. He has a knack for delivering seemingly complicated ideas with clarity and charm. He is also a brilliant expositor. See Milnor's article on his work here.
A: John Baez. "This week's finds in mathematical physics" is a great playground for young mathematicians.  I was a graduate student when I first found it, and I really loved the links between various TWFs and the math they discussed.  Not only does he show you the breadth of modern math, he also gives you bridges between the various areas.  
A: Sir Michael Atiyah. 
Besides his great technical work (his collected papers are absolutely magnificent!) especially his great interview "Beauty in Mathematics" was very inspiring to me. Another inspiring piece is his "Advice to a Young Mathematician" in the Princeton Companion to Mathematics.
A: Serge Lang's Algebra was my first serious encounter with mathematics, the event was a very singular defining moment in my life.
Back then, I was firmly intent on becoming a poet or, at least, pursuing some kind of literary career. Like most budding poets, I loved books and I liked spending time in the library. I was very curious, I would often wander in a section and pick up a book just to see what that row was about. One day I picked up an old rebound copy of Lang's Algebra. It was dirty purplish grey and it just said Lang: Algebra in half erased white letters. I don't think I had any good reason to pick up that book, it certainly wasn't very attractive, I probably just wondered why one would write such a large tome on algebra. I sat down with the book and read the first page where he defines a monoid and proves the uniqueness of the identity element. I was fascinated. It was so beautiful. I fell in love.
I don't think I read much of Lang's book on that day, I probably only had an hour or less to spare, but I went back to the math section later and I picked up more books. The next one was Willard Van Orman Quine's Set Theory and its Logic, which is probably the worst possible way to get introduced to Set Theory but that's how I eventually became a logician instead of a poet.
A: Herbert Federer: his work on geometric measure theorey radiacally changed my view on differential geometry. Besides that, it is extremely practical when studying geometric flows.
A: John Milnor too many great books.
Friedhelm Waldhausen for his papers on three manifold topology.
William Thurston for his lecture notes on hyperbolic three manifolds.
Fathi, Laudenbach and Poeneru for "Travaux de Thurston"
Atiyah and Bott, for "Yang-Mills on Riemann Surfaces."
Kobayashi for "Differential Geometry of Complex Vector Bundles"
Bill Meeks for his lecture notes on Minimal Surfaces.
A: John Willard Milnor for his books about "Morse Theory" and the "h-cobordism theorem" (I think it is a crime that it isn't printed anymore) and for writing papers in a way that they are quite self-contained and readable.  
A: Does Martin Gardner count, even though he is not a mathematician?
I read all of the "Mathematical Games" columns in Scientific American when I was maybe 12 or 14.  And this was a non-trivial task ... I would ride my bicycle to the public library one afternoon a week to read a few more columns (the school library didn't have it).  So it took maybe a year to read them all.
A: Carl Friedrich Gauss.
The breadth and beauty of his work amazed me when I was a student, and it still inspires me.  
He started by building on much less than what many of us take for granted: His doctoral dissertation was the Fundamental Theorem of Algebra. His work covered deep, essential results in many areas, from number theory (quadratic reciprocity, conjecture of prime number theorem) to geometry (Gaussian curvature) to statistics (least squares) to probability (Gaussian distribution). It is difficult to imagine these areas without his fundamental contributions. He also contributed to physics and astronomy. 
Even though Gauss explored many areas, he took the time to revisit old results, looking for different and more satisfactory proofs. 
A: Who: Leonhard Euler.
When: As a highschool student.
Where: On the book "Euler: the master of us all" by William Dunham.
Why: The amount of creativity and genius dispersed among the so-different works of Euler continues to amaze me just now, so it only could have a devastating effect on me 10 years ago. He not only addressed a lot of distinct topics, he layed the foundations of many branches of mathematics and solved with ease many problems that were interesting me at that moment of my life. I learned a lot from him: he really deserves the title of "master of us all".
A: I should say three of them:
a. Philippe Flajolet
His work on analytic combinatorics inspired me enough to decide to study mathematics further after having majored in theoretical computer science. He wrote a book along with Sedgewick called analytic combinatorics, not to mention lots of papers on analysis of algorithms using the techniques he developes, he's a Cauchy of modern combinatorics.
b. Lucjan Jacak
Mathematician & quantum physicist, his lectures from quantum physics have inspired me to study this field for over two years. His most famous work concers quantum dots.
c. Bollobas, Kozma, et. al
And their work on non-constructive, probabilistic methods in graphs, also neuropercolation theory etc. Somewhat a revolutionary idea.
A: Simon Donaldson. His proofs involve (to quote wikipedia) a creative use of analysis. I loved his proof of the theorem of Narasimhan and Seshadri.
A: Erdős
Sophomore year when I decided that I didn't like physics classes I just happened to be reading "The Man Who Loved Only Numbers" by Hoffman. Between this and "How to Read and Do Proofs" by Solow, I saw mathematics as something much more beautiful. This combined with reading about Erdos style of mathematics made me really attracted to research and led to my first REU experience. It was all downhill from there.
A: Albert H Beiler. When I was in high school, someone gave me his book, Recreations in the Theory of Numbers. So different from any mathematics I had seen before, and so much fun! From there, it was just a short step to the Ross program....
A: JH Conway. He has published work in a diverse set of interesting fields. I first met his name when looking for cool computer programs to write as a kid (ie. the Game of Life) but since then his name kept appearing in mathematics that I found interesting, whether it's Monstrous Moonshine or the properties of finite state automata. He has this incredible knack for turning anything he touches into fun - whether it's knot theory, group theory, quadratic forms, or, more obviously, combinatorial games. As well as working at the frontiers of mathematics he's discovered accessible but surprising and beautiful recreational mathematics, like Conway's soldiers. All in all, an amazing guy. Once of my regrets in life is being too lazy to attend his lectures on finite simple groups when I was an undergraduate.
A: Gian-Carlo Rota. I really wish I could pinpoint the moment that I came across some of his work, but I can't. And I've only just begun graduate work so it's impossible to be really honest about what sort of impact he has had on me... only time can tell.
But nonetheless, his writings are truly inspiring. It's tough to describe the wonder they have given me. Rota began as a functional analyst (PhD under Jacob Schwartz, of the Dunford & Schwartz fame) and moved over to algebraic combinatorics in the 1960s. One of his first papers that has stuck in my mind is "The Number of Partitions of a Set" in which he applies the techniques of the so-called 'umbral calculus' (which he also worked to rigorously formulate) to beautifully establish some combinatorial results. He's credited as setting the field of algebraic combinatorics on solid ground via his seminal papers On the Foundations of Combinatorial Theory. But it's not just the technical results -- his writing is just plain fun to read. 
Given my personal interests, I really appreciate that although Rota did so much work in combinatorics he always seemed to lean back towards his roots in functional analysis & probability. In fact, his goal to find the true nature of classical results in analysis and probability led him to a great deal of good work in combinatorics, e.g. his work on the Rota-Baxter algebra inspired by his ambition to understand "the algebra of indefinite integration", and his work on the foundations of probability with the ambition to understand the middle ground between the discrete and the continuous. Moreso than most people he is willing to put his position out there and speak about mathematics rather than just speak mathematics. A great example of this is his book "Indiscrete Thoughts" -- definitely worth reading. You may not agree with many things he says but it's wonderful to be allowed a glimpse into the mind of a man such as Rota.
A: Poincaré. Not so much for his mathematical writings (although what I've found in English, or struggled through in French, has been uniformly interesting [if dated, and/or, um, in a language I barely understand]) but for his thoughts on the philosophy and psychology of math. After the already-mentioned John Baez, the first thing I'll implore anyone who bothers to ask to read is "Intuition and Logic in Mathematics," fin-de-siecle thinking and all.
A: Bernhard Riemann.
The idea of the Riemann Surface and manifolds stroke me when I was a high school student. 
A: Silvanus P. Thompson: "Calculus Made Easy"  (old simian proverb... "what one fool can do, so can another").
A: The graduate advisor at Queens College of the City University Of New York, Nick Metas, was and continues to be my greatest influence.
I first had a conversation on the phone with Nick over 15 years ago when I was a young chemistry major taking calculus and just becoming interested in mathematics. We spoke for over 3 hours and we were friends from that moment on.
It was Nick who indocrinated me into the ways of true rigor through his courses and countless conversations,and the equal cardinality of the stories he's told. Nick is a true scholar and my enormous knowledge of the textbook literature and research papers from the 1960's onward,I learned from Nick.My learned capacity for self-learning got me through the lean years at CUNY during my illnesses,when there wasn't much of a mathematics department there.
In relation to the reference to Gian-Can Rota above,I am Rota's mathematical grandson through Nick. Nick loved Rota and his eyes light up when he speaks of his dissertation advisor and friend from his student days at MIT. I hope someday there's someone famous I can feel that way about. But no one's influenced me more then Nick. 
Nick's has been my friend and advisor for all things mathematical and he celebrated his 74th birthday yesterday quietly in his usual office hour,with dozens of students asking him for advice or just listening to his wonderful stories and jokes. Regardless of what happens,it will be Nick who's influence on me as a mathematician, student and mentor who's shaped me the most. 
A: *

*Paul Cohen & Kurt Gödel

*

*They gave us the tools to construct models of set theory.


*Kenneth Kunen

*

*His book "Set theory: An Introduction To Independence Results" was the book that got me interested in the field I would later call my home.


*Saharon Shelah

*

*His work on forcing, and singular cardinals keep me asking questions, and open up the possibility for questions I didn't even know could be asked.


A: As a graduate student, it's hard to say who's influenced me the most. Certainly my advisor seems to be a strong candidate, though others mentioned above have also influenced me. Still, there is an individual who has influenced my mathematical development at several different times in my career so far and who deserves a mention. From my talks with other grad students, I know I am not alone in being grateful for this person's work and his clear way of thinking and writing about mathematics.
Who: Keith Conrad
Which work: his body of expository papers at http://www.math.uconn.edu/~kconrad/blurbs/
When/Why: First, sophomore year of undergrad, in an elementary number theory course. This course and Professor Conrad's writings helped convince me to go to grad school. Then also junior year when I saw him give a talk at a conference and later at my own college. And more recently in the first year of grad school when I learned about tensor products, modules, exterior algebras, Galois theory, and several other topics.
A: Who: G. H. Hardy
When: As a high school student
Where: The book "Pure Mathematics" -- from which I learned real analysis.
Who: Serge Lang
When: As a college student
Where: At Columbia, Serge Lang was my mathematical mentor.  I took Math I C/II C from him (which I'd describe as freshman mathematics for prospective Ph.D.'s -- it was pretty much an undergraduate Abstract Algebra, plus Real Analysis plus more in two semesters).  His energy and love of mathematics was inspiring.  I know that nobody who met him felt neutral about him.  He was incredibly dedicated to his students.  If he liked you he would move mountains.
Who: Lipman Bers
When: As a college student
Where: At Columbia, Lipman Bers was my other inspiration.  I took Math III C/IV C from him -- sophomore mathematics for prospective Ph.D.'s.  Besides being a very lucid lecturer, with fantastic geometric intuition, he was sophisticated and kind -- a prince among men!  By example he showed how one could live a mathematical life (at perhaps a bit less than the frenetic pace of Serge Lang).
A: Gödel I was captivated by his belief of a platonic mathematical world and the belief that human can understand such a thing.
A: Srinivasa Ramanujan. He does not figure that much in my work right now. But studying his notebooks (via Bruce Berndt's studies) when I was a teenager taught me how to appreciate beautiful mathematics. From that moment on, I was hooked. I knew I had to be a mathematician.
As for those whose lives or personalities inspired me, or whose style of thinking influenced my methodology, too many to count...
A: Cliched perhaps, but my fellow graduate students when I was in grad school. They're the ones that answered my questions when I got lost, shared their half-baked ideas and listened to mine, showed me just how many interesting fields of math there are and how many different perspectives people can have on the same subject, and cheered me on when things were difficult.
A: G.H. Hardy.  Reading "A Mathematician's Apology" in high school really changed the way I think about mathematics.
A: Henry Ernest Dudeney, author of Amusements in Mathematics, another book that set me, in my early teenage years, on the path to mathematics. 
A: (I think that for a question like this with the answers being entirely personal, the voting is of little or no significance.)
For me there are so many that I hardly know where to begin. Initially, Martin Gardner. Among those I knew personally: my undergrad profs (espcially I.M. Singer) who taught me what math is.  Then Bill Thurston, with whom I shared an office in grad school.  Stephen Smale, my de facto co-thesis advisor.
Notably Gauss, Riemann, Klein, Poincaré, Milnor.
Above all, my thesis advisor, Morris Hirsch, with whom I've had a continuing connection since 1970.
A: I would have to say equal parts Godel and Raymond Smullyan.  When I first started caring about math I picked up both Newman and Nagel's book on the Incompleteness Theorems and Smullyan's "First Order Logic".  I then bought as many of the Smullyan puzzle books I could find.  I also read Smullyan's "The Tao is Silent", which influenced me as a person.
A: I was an (computer systems) engineering student, I decided tu study Mathematics after reading "Whom the gods love" it's a book about the life of Évariste Galois. I was thinking about that but reading that book gave me the courage. I also feel that mathematics is not very different from the topics I like about computer science.
A: Consider looking forward: Grisha Perelman, his strange history
 wiki G.Perelman. However the first millenium prize awarded. Even note this: Terence Tao said... "well, it's amazing"
A: In terms of style of math, I'm not quite sure yet. However, I think that it is certainly true for me, and no doubt for countless others, one's advisors role is one of the most crucial influences one may have.
A: Colin Adams
Knot theory was the first topic I was really excited about as an undergraduate from reading "The Knot Book."  I did an summer program with Colin Adams and got my first glimpse of research, even at an undergraduate level and realized it's what I wanted to do for the rest of my life.
A: Dieudonné
The number 1 personality behind Bourbaki.  Even though he was famous for taking the most extreme positions and was widely dismissed as a radical, his vision of mathematics is one that has largely been adopted by almost all mathematicians everywhere.  Reading any piece of mathematical work he wrote, it his hard not to feel the respect and passion he felt for mathematics as a subject.
Dan Kan
Singlehandedly developed categorical homotopy theory into a full-fledged replacement for the homotopy theory of spaces (Kan complexes, combinatorial homotopy groups, subdivision, $Ex^\infty$, among many other things) as well as a large part of the foundations of homological algebra (Dold-Kan correspondence), category theory (adjoint functors, Kan extensions), and the modern theory of simplicial localization (with Dwyer) among numerous other achievements.  
It's said that Kan's breakthrough paper on adjoint functors convinced Eilenberg and Mac Lane that pure category theory was not only a viable mathematical discipline (rather than a language), but also a deep and rich one.  
A: Otto Forster.
He is the most brilliant expositor I have ever met. I cherish the notes I took a long time ago of courses he gave in Italy and France, in perfect Italian and French.
He wrote a wonderful course on Analysis (in three volumes) which has been the reference in German Universities for 30 years, something like Rudin in the States.
His book on Riemann surfaces (both compact and non compact) is a masterful blend of Algebra, Topology and Analysis, with tools ranging from cohomology of sheaves to difficult potential theory.
He is a brilliant researcher and has made important contributions to complex geometry and also to algebra (Forster-Swan).
Working with him was a wonderful experience and he had the generosity of letting me co-sign 
articles to which my contribution was negligible compared to his.
I am very happy of this opportunity to express my gratitude to and admiration for this genuine scholar and real gentleman.
A: Richard Courant. Several years before I started studying mathematics in earnest, I spent a summer working through his calculus texts. Only recently, on re-reading them, have I come to realize how much my understanding of calculus, linear algebra, and, more generally, of the unity of all mathematics and, to use Hilbert's words, the importance of "finding that special case which contains all the germs of generality," have been directly inspired by Courant's writings.
From the preface to the first German edition of his Differential and Integral Calculus:

My aim is to exhibit the close connexion between analysis and its applications and, without loss of rigour and precision, to give due credit to intuition as the source of mathematical truth. The presentation of analysis as a closed system of truths without reference to their origin and purpose has, it is true, an aesthetic charm and satisfies a deep philosophical need. But the attitude of those who consider analysis solely as an abstractly logical, introverted science is not only highly unsuitable for beginners but endangers the future of the subject; for to pursue mathematical analysis while at the same time turning one's back on its applications and on intuition is to condemn it to hopeless atrophy. To me it seems extremely important that the student should be warned from the very beginning against a smug and presumptuous purism; this is not the least of my purposes in writing this book.

Another example: while not a "linear algebra book" per se, I have yet to find a better introduction to "abstract linear algbera" than the first volume of Courant's Methods of Mathematical Physics ("Courant-Hilbert"; so named because much of the material was drawn from Hilbert's lectures and writings on the subject). His one-line explanation of "abstract finite-dimensional vector spaces" is classic: "for n > 3, geometrical visualization is no longer possible but geometrical terminology remains suitable."
Lest one be misled into thinking Courant saw "abstract" vector spaces as "$\mathbb{R}^n$ in a cheap tuxedo," he introduces function spaces in the second chapter ("series expansions of arbitrary functions"), and most of the book is about quadratic eigenvalue problems, or, as Courant saw it, "the problem of transforming a quadratic form in infinitely many variables to principal axes."
As a final example: Courant's expository What is Mathematics? is perhaps best described as an unparalleled collection of articles carefully crafted to serve as an object at which one can point and say "this is." Moreover, while written as a "popularization," its introduction to constrained extrema problems is, without question, a far, far better introduction than any textbook I've ever seen.
I should also mention Felix Klein, not only because Klein's views on "calculus reform" so clearly influenced both the style and substance of Courant's texts, but since a number of Klein's lectures have had an equally significant influence on my own perspective. For those unfamiliar with the breadth of Klein's interests, I'm tempted to say "his Erlangen lecture, least of all" (not that there's anything wrong with it).
Lest my comments be mistaken for a sort of wistful "remembrance of things past," I'd easily place Terence Tao's writings on par with Courant's, for many of the same reasons: clear and concise without being terse, straightforward yet not oversimplified, and, most importantly, animated by a sort of — je ne sais quoi — whatever it is, it seems to involve, in roughly equal proportions: mastery of one's own craft, a genuine desire to pass it on, and the considerable expository skills required to actually do so.
Finally, I can't help but mention Richard Feynman in this context, and to plug his Nobel lecture in particular. While not a mathematician per se, Feynman surely ranks among the twentieth century's best examples of a "mathematical physicist" in the finest sense of the term, not merely satisfied by a purely mathematical "interpretation" of physical phenomena, but surprised, excited, and, dare I say, delighted by the prospect! Moreover, he was equally excited about mathematics in general, see, e.g., the "algebra" chapter in the Feynman Lectures on Physics.
A: Arnold Ross. He ran the summer program in Number Theory for high school students at Ohio State University, my first exposure to serious mathematics. His lectures set me on a course from which I've hardly deviated in over 40 years. 
A: Benedict Gross. I saw him lecture a few times on BSD. His enthusiasm and mastery were very inspirational. It reminded me why I want to be a professional mathematician. I had just finished my general exams the previous semester and felt tired from taking so many classes and preparing for exams. It had put a haze over the beauty of mathematics. Professor Gross made it clear again.
A: Leibniz.  Not just for his mathematics (calculus, amazing insights in logic, semantics) but he was just an incredible polymath, with deep work in law, history, linguistics, chemistry, physics, metaphysics, politics, engineering, sociology, he founded 'library science', and on and on. 
A: Raymond Smullyan, in elementary school.  His book "Alice in Puzzleland" was a childhood favorite of mine and is what and inspired a life long interest in math.
A: Vladimir Igorevich Arnold.
A: Alexander Grothendieck.
See, for example, his passage about opening a nut.  This was very inspiring for me and was one of the key reasons
that led me to abandon computer science and start studying math.
I also very much like the way he uses geometric intuition in algebraic geometry, it helped me a lot and not only in algebraic geometry.
A: Who: H. S. M. Coxeter.
When: When I was an undergraduate.
Why: Not only was he a prince among mathematicians, but he was also a gentleman of the first rank.  Several of his books also inspired me.  Moreover, by transitivity, he was (for me) clearly the most influential.
A: Who: Manin, Parshin, Serre, Tate.
When: When I was an undergraduate.
A: Nigel Hitchin has an amazing ability to find a new mathematical structure out of every physical context. His articles and papers are always clear, concise and provide the necessary intuition for the reader to grasp the concept/application while reading the definitions. I have always felt that many mathematics papers ignore the reader and focus on presenting things in such a concise matter that the true meaning is obfuscated. Hitchin never seems to do that and almost holds the reader's hand as he guides him/her through the wonders of mathematical physics. 
A: Taking into account the butterfly effect, I guess Roger Penrose would have influenced me the most. At first I was into physics and taught myself some calculus to understand it better; but it was more a tool than an end in itself. Then, at about 14, I read The Emperor's New Mind and was totally blown away by the ideas and proofs around Gödel's and Turing's work. Previously I had no idea the human mind could be so powerful!
It definitely pushed me into mathematics, and to this day I am very logically and discretely inclined.
A: who: Maxim Kontsevich
when: when I was a PhD student, and onwards. 
why: probably because of my main research interest when I was a PhD student, namely deformation quantization. Also because before moving to (many) other subjects Kontsevich has formulated a lot of very reasonnable conjectures and guessed a lot of possible developpments in the field. Some of them I have been following. Even now, I am still thinking quite often about a few questions he raised . 
A: Dedekind, whose championing of concepts (vs. calculation) left a longstanding impression on the way that I conceive mathematics - even long after I first started reading the masters as a student.  Back then I had to grovel through the bowels of the MIT libraries but now, with many important historical works easily accessible online, there is no excuse not to read the masters.
A: Walter Rudin: His texts in Analysis are the ones which got me into mathematics. 
A: Barry Mazur. The Eisenstein ideal paper, the one on towers of abelian varieties, as well as his beautiful expositions on visibility, Galois deformations, Kolyvagin systems etc continue to inspire me everyday.
A: Charles Sanders Peirce, his Collected Papers, first encountered in the less-traveled Library of Congress from B to BD corner of the math library my freshman year, and compelling me to the prodigal expense of $35.00 in late 1960-ish dollars to buy Volumes 3 & 4 bound as 1.  Every year that goes by is a year I add to the number of years his thought was ahead of his time.
A: Louis Comtet, through his book "Analyse Combinatoire vol 1 and 2", now republished in english translation with additions and corrections as "Advanced Combinatorics".
When ? My first year in Paris University while I was attending boring courses in Analysis and Linear Algebra that were very inferior to what I have been exposed in high school the year before.
These two little pocket books were relatively easy and cheap to find and gave a wealth of packed information and links to the existing litterature on combinatorics. Combinatorial Mathematics were not in fashion in France in the 1970s, neither in the 1980s. Among many things I liked were the fancy notations, the diagrams, the density of results, the careful index, the intersection with so many other mathematical theories such as set theory, differential equations, topology, group theory. And it was also my first contact with a slightly formalized graph theory, Eulerian numbers, integer partitions, multiple summation, etc.
A: Lou van den Dries
Frankly speaking.
A: The first inspiration was Gauss's solution of sum of first n natural numbers when i was in high school...I went on to learn his notion of congruence etc which were really breath taking at that time.
