Austrian-born British philosopher Ludwig Wittgenstein was BOTD in 1889. Born in Vienna (then part of the Austro-Hungarian Empire) to a wealthy industrialist family, he grew up at the centre of late 20th century Viennese society, as his parents entertained Gustav Klimt, Sigmund Freud,  Johannes Brahms and Gustav Mahler. Three of his siblings committed suicide while he was still in his teens – in 1904, his brother Rudi left a suicide note despairing of his “perverted disposition”. Intent on becoming an engineer, he moved to England in 1908 to study aeronautics, though became fascinated by the philosophy of mathematics. He relocated to Cambridge University to study with the philosopher Bertrand Russell, who declared after a year that he had nothing left to teach him. Wittgenstein moved to Norway, building himself a wooden hut by a fjord, where he worked on his “picture theory of meaning”, positing that logic is inexpressible and that there are no logical facts or logical truths. At the outbreak of World War One, he returned to Vienna and enlisted in the Austrian army, hoping that the experience of confronting death would help him concentrate his thoughts. While fighting at the Russian front, he experienced a religious conversion, concluding that moral truths, while inexpressible, made themselves manifest by the fact of their not being expressed. He published his theories in 1921’s Tractatus Logico-Philosophicus, which became hugely influential on post-war philosophers. Convinced that he had solved all the essential problems of philosophy, Wittgenstein trained as a schoolteacher, and became infamous for dispensing harsh corporal punishment on his male and female students. Happily, he was lured back to Cambridge in 1929, where he was appointed a lecturer and made a fellow of Trinity College. He rejected his earlier theories, concluding that philosophy was a method of clearing up confusions that arise through misunderstandings of language. He spent the next 20 years refining his theories of meaning, refusing to publish his findings and encouraging his students to become doctors, gardeners or shop assistants. During World War Two, he worked as a porter in a London hospital and later as a medical research assistant. After the war, he moved to Ireland, returning to Cambridge when he learned he had terminal cancer. He died in 1951, aged 62. His manuscript Philosophische Untersuchungen (Philosophical Investigations) was published posthumously in 1953. Now considered one of most important philosophers of the 20th century, his ideas had a profound impact on the development of semiotics and post-structuralist theory. Wittgenstein identified as homosexual, but appears to have had no intimate relationships. His letters and diaries revealed his strict self-imposed division between human love (which he approved of) and sexual desire (which he claimed to despise). He was portrayed by Karl Johnson in Derek Jarman‘s surprisingly funny 1993 biopic Wittgenstein.