Confessions of a Philosopher, by Bryan Magee, p 208-209:
When I [Bryan Magee] asked him [Bertrand Russell] who he regarded as the greatest man he had ever met, he needed longer to consider his reply. In the end he came up with Lenin. When I asked why, he said it was because Lenin combined a brilliant mind with genius-level ability as a man of action, and this gave him extraordinary stature and effectiveness as a person. Also, he had changed the entire course of world history in a way few individuals ever do. However, he added, Lenin was not in the least morally admirable: he came near to boasting about the enormous scale of the death and suffering he was causing, and laughed about it in conversation with Russell.