"Hermann Graßmann submitted [Die lineale Ausdehnungslehre] as a Ph. D. thesis, but Möbius said he was unable to evaluate it and forwarded it to Ernst Kummer, who rejected it without giving it a careful reading."
From a webpage : "His 1844 work Die lineale Ausdehnungslehre: Ein neuer Zweig der Mathematik [The Theory of Linear Extension, a New Branch of Mathematics], effectively single-handedly founded Linear Algebra. This work was submitted as a Ph.D. thesis in Mathematics, however its formulation of linear vector space in opposition to the canonical Euclidean geometry of the time was too radical for his contemporary mathematics establishment and was rejected. Consequently, the significance of contribution to the mathematical sciences were largely unrecognized in his lifetime, but they were eventually re-discovered towards the end of the nineteenth century and early twentieth century. It was because of these rejections and early lack of recognition of his work in the mathematics that he suffered he turned himself to Vedic studies, and made those discoveries in there which we know him best for [!]" -- Hermann Graßmann: Philologist and Mathematician
The claim about "single-handedly founding linear algebra" seems exaggerated. For a closer investigation, one might e.g. look at the articles by D. Fearnley-Sander quoted and referenced in the wikipedia article.
