Joseph Rotblat passed away on Wednesday, reports The Guardian.
[Rotblat] joined the Manhattan project, in the belief that a nuclear bomb was the only realistic deterrent against the Nazis who were also pursuing the bomb.
"In 1944, when I learned the Germans had given up the project, the whole rationale for my being there disappeared," Sir Joseph told the Guardian this year.
He became the only scientist to resign from the project and was accused by the US of being a spy.
Rotblat later co-founded the Pugwash conferences, a movement that worked behind the scenes, chiefly during the cold war, to discourage the use and proliferation of nuclear weapons. The group's efforts were acknowledged in 1995 when Sir Joseph and the Pugwash group won the Nobel peace prize.