Austrian philosopher, lived 1889-1951. Best known for his concept of “language games” and the idea that “the meaning of a word is its use in the language” - essentially, figuring out what an utterance “means” is not a matter of logical propositions and their formal connections, but of the utterance's intended effect within a certain social context. These ideas developed into the theory of speech acts. Natural language, for Wittgenstein, is a set of specific language games connected together by “family resemblances” to form something more general.
Wittgenstein was born into a very rich and very unhappy family in Vienna. Three of his four brothers committed suicide, and he himself was known to be quite a melancholy person. He moved to Cambridge in 1929 and received a PhD (using the Tractatus as his thesis), eventually becoming a professor of philosophy there. He is known to have had several discussions with Alan Turing when Turing was a student at Cambridge, and it seems that Turing spoke as an intense defender of mathematical formalism.