Bertrand Arthur William Russell [Third Earl Russell] (1872-1970) was a mathematician, philosopher, and activist. He declared himself an agnostic, but he might also be described as a weak atheist. He was strongly critical of Christianity and irrationalism in general, writing books like "Why I Am Not a Christian".
My conclusion is that there is no reason to believe any of the dogmas of traditional theology and, further, that there is no reason to wish that they were true. Man, in so far as he is not subject to natural forces, is free to work out his own destiny. The responsibility is his, and so is the opportunity. -- Bertrand Russell, "Is There a God?" commissioned by, but never published in, Illustrated Magazine (1952: repr. The Collected Papers of Bertrand Russell, Volume 11: Last Philosophical Testament, 1943-68, ed. John G. Slater and Peter K