Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS , was a philosopher, historian, logician, mathematician, advocate for social reform, and pacifist. Although usually regarded as English, he was born in Wales.

A prolific writer, he was a populariser of philosophy and a commentator on a large variety of topics. Continuing a family tradition in political affairs, he was a prominent anti-war activist, championing free trade between nations and anti-imperialism. He authored the essay On Denoting and was co-author of Principia Mathematica, an attempt to ground mathematics on the laws of logic. Both works have had a considerable influence on logic, set theory, linguistics and analytic philosophy.