Moritz Nähr · Public domain

Wrote two philosophies, the second demolishing the first, and both dominate the field a century later. The Tractatus argued that most of what philosophy discusses cannot meaningfully be said; having settled that, he gave away an enormous inherited fortune and went to teach primary school in rural Austria. He returned to Cambridge and spent his later years on the Philosophical Investigations, which treats meaning as something built out of use rather than reference. Three of his four brothers killed themselves.