Bertrand Arthur William Russell, 3rd Earl Russell, was a British philosopher, logician, mathematician, and public intellectual. He influenced mathematics, logic, set theory, and various areas of analytic philosophy. Russell was one of the early 20th century's prominent logicians and a founder of analytic philosophy, alongside his predecessor Gottlob Frege, his friend and colleague G. E. Moore, and his student and protégé Ludwig Wittgenstein. Russell, with Moore, led the British "revolt against idealism". Together with his former teacher A. N. Whitehead, he wrote Principia Mathematica, a milestone in the development of classical logic.

Russell was a pacifist who championed anti-imperialism, and chaired the India League. He went to prison for his pacifism during World War I and initially supported appeasement against Adolf Hitler's Nazi Germany, before changing his view in 1943, describing war as a necessary "lesser of two evils". In the wake of World War II, he welcomed American global hegemony in preference to either Soviet hegemony or ineffective world leadership, even if it meant using nuclear weapons. He later criticized Stalinist totalitarianism, condemned the United States' involvement in the Vietnam War, and became an outspoken proponent of nuclear disarmament.

In 1950, Russell was awarded the Nobel Prize in Literature "in recognition of his varied and significant writings in which he champions humanitarian ideals and freedom of thought". His work has had a significant impact on fields including mathematics, logic, set theory, artificial intelligence, cognitive science, computer science, philosophy of language, epistemology, metaphysics, ethics, and politics.