Bertrand Russell was a controversial public figure throughout his long and extraordinarily active life. He was born in Trelleck, Gwent; his parents died when he was very young and he was brought up by his grandmother, the widow of Lord John Russell, the Liberal Prime Minister and 1st Earl. He was educated privately and at Trinity College, Cambridge, where he took first-class honours in mathematics and philosophy. He graduated in 1894, was briefly attaché to the British Embassy in Paris, and became a Fellow of Trinity in 1895, shortly after his marriage to Alys Pearsall Smith.
His most original contributions to mathematical logic and philosophy are generally agreed to belong to the period before World War I, as expounded in The Principles of Mathematics (1903), which argues that the whole of mathematics could be derived from logic, and the monumental Principia Mathematica (with Alfred North Whitehead, 1910-13), which worked out this programme in a fully developed formal system and stands as a landmark in the history of logic and mathematics. Russell's famous 'theory of types' and his 'theory of descriptions' belong to this same period.
Ludwig Wittgenstein went to Cambridge to be his student from 1912 to 1913 and began the work that led to the Tractatus (No Suggestions) (1922), for the English version of which Russell wrote an introduction. He wrote his first genuinely popular work in 1912, The Problems of Philosophy, which can still be read as a brilliantly stimulating introduction to the subject. Politics became his dominant concern during World War I and his active pacifism caused both the loss of his Trinity fellowship (1916), and his imprisonment (1918), during the course of which he wrote his Introduction to Mathematical Philosophy (1919).
He had now to make a living by lecturing and journalism, and became a celebrated controversialist. He visited the USSR, where he met Lenin, Trotsky and Gorky, which sobered his early enthusiasm for Communism and led to the critical Theory and Practice of Bolshevism (1919). He also taught in Beijing (1920-21). In 1921 he married his second wife, Dora Black, and with her founded (in 1927) and ran a progressive school near Petersfield; he set out his educational views in On Education (1926) and Education and the Social Order (1932).
In 1931 he succeeded his elder brother, John, 2nd Earl Russell, as 3rd Earl Russell. His second divorce (1934) and marriage to Patricia Spence (1936) helped to make controversial his book Marriage and Morals (1932); and his lectureship at City College, New York, was terminated in 1940 after complaints that he was an 'enemy of religion and morality', although he later won substantial damages for wrongful dismissal. The rise of Fascism led him to renounce his pacifism in 1939; his fellowship at Trinity was restored in 1944, and he returned to England after World War II to be honoured with an Order of Merit, and to give the first BBC Reith Lecture in 1949. He was awarded the Nobel Prize for literature in 1950.
He had meanwhile continued publishing important philosophical work, mainly on epistemology, in such books as The Analysis of Mind (1921), An Enquiry into Meaning and Truth (1940) and Human Knowledge Its Scope and Limits (1948), and in 1945 published the bestselling History of Western Philosophy. He also published a stream of popular and provocative works on social, moral and religious questions, some of the more celebrated essays later being collected in Why I am not a Christian (1957).
After 1949 he became increasingly preoccupied with the cause of nuclear disarmament, taking a leading role in CND (Campaign for Nuclear Disarmament) and later the Committee of 100, and engaging in a remarkable correspondence with various world leaders. In 1961 he was again imprisoned, with his fourth and last wife, Edith Finch, for his part in a sit-down demonstration in Whitehall. His last years were spent in North Wales, and he retained to the end his lucidity, independence of mind, and humour. The last major publications were his three volumes of Autobiography (1967-69).