Serge Lang. Lang's '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. As 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 the 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.