Bertrand Russell
He greatly contributed to the development of mathematical logic and its use in philosophical analysis. He advocated the logicist thesis that mathematics can be reduced to logic, and in the process of developing and defending this thesis, he devised his theories of descriptions and of types. And he himself discovered a paradox (Russell's Paradox; see the picture) which was to become an obstacle to the success of logicism.
He also wrote on almost every topic in philosphy, and engaged in various kinds of activities through his long career.
