Ludwig Josef Johann Wittgenstein (26 April 1889 – 29 April 1951) was an Austrian-British philosopher who worked primarily in the areas of logic, philosophy of mathematics, philosophy of mind, and philosophy of language.
Described by his mentor and colleague Bertrand Russell as "the most perfect example I have ever known of genius as traditionally conceived, passionate, profound, intense, and dominating," Wittgenstein is considered by many to be the greatest philosopher of the 20th century. Instrumental in inspiring two of the century's principal philosophical movements, logical positivism and ordinary language philosophy, he is considered one of the most important figures in analytic philosophy. According to an end of the century poll, professional philosophers rank both his Tractatus Logico-Philosophicus (1921) and Philosophical Investigations (1953) among the top five most important books in twentieth-century philosophy, the latter standing out as "the one crossover masterpiece in twentieth-century philosophy, appealing across diverse specializations and philosophical orientations." Wittgenstein's influence has been felt in nearly every field of the humanities and social sciences, yet there are widely diverging interpretations of his thought.