Richard Feynman is a wholly influential theoretical 20th century physicist. He performed extensive work in the field of quantum mechanics; he is well known for his quote "If you think you understand Quantum Theory you don't understand it". He also had an interest in Microbiology. He was an atheist, with some strong views on Christianity in general. Quantum Theory in general proposes some reason to believe that some selected things can occur without a cause. Some of the work Feynman did tested these various hypotheses. Quantum Theory in general, especially those parts of it investigated by Richard Feynman, is a common objection to the Kalam Cosmological Argument.
For more information, see the wikipedia article: http://en.m.wikipedia.org/wiki/Richard_Feynman