Andrei Sakharov (1921-1989) was a Soviet physicist who became, in the words of the Nobel Peace Committee, a spokesman for the conscience of mankind. He was fascinated by fundamental physics and cosmology, but first he spent two decades designing nuclear weapons. He came to be regarded as the father of the Soviet hydrogen bomb, contributing perhaps more than anyone else to the military might of the USSR. But gradually Sakharov became one of the regime’s most courageous critics, a defender of human rights and democracy. He could not be silenced, and helped bring down one of history’s most powerful dictatorships.