Yes, J. Robert Oppenheimer, often referred to as the "father of the atomic bomb," is known to have expressed significant regret over his role in developing nuclear weapons. His regret was chronicled in his famous quoting from the Bhagavad Gita after the first successful test of the atomic bomb in 1945: "Now I am become Death, the destroyer of worlds." In later life, Oppenheimer became a proponent of arms control and opposed the development of the hydrogen bomb.