Brian Todd O'Leary (January 27, 1940 – July 28, 2011) was an American scientist, author, and former NASA astronaut. He was a member of the sixth group of astronauts selected by NASA in August 1967. The members of this group of eleven were known as the scientist-astronauts, intended to train for the Apollo Applications programme - a follow-on to the Apollo Program, which was ultimately canceled. In later life he became an advocate of utilising exotic energy sources to resolve humanity's energy problems.