Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS (18 May 1872 – 2 February 1970), was a British philosopher, logician, mathematician, historian, pacifist, and social critic. Though he spent most of his life in England, he was born in Wales, and died there at the age of 97.

Russell led the British "revolt against idealism" in the early 1900s. He is considered one of the founders of analytic philosophy along with his predecessor Gottlob Frege and his protégé Ludwig Wittgenstein, and is widely held to be one of the 20th century's premier logicians. He co-authored, with A. N. Whitehead, Principia Mathematica, an attempt to ground mathematics on logic. His philosophical essay "On Denoting" has been considered a "paradigm of philosophy." His work has had a considerable influence on logic, mathematics, set theory, linguistics, and philosophy, especially philosophy of language, epistemology, and metaphysics.

Russell was a prominent anti-war activist; he championed free trade and anti-imperialism. Russell went to prison for his pacifist activism during World War I. Later, he campaigned against Adolf Hitler, then criticised Stalinist totalitarianism, attacked the United States of America's involvement in the Vietnam War, and finally 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."