In quantum theory, a particle's state can never be precisely measured or predicted. In Everett's interpretation, these uncertainties produce many alternate worlds, sprouting infinitely like a many-headed tree. He believed that we could be living in just one of countless such alternate realities. In one universe McCain wins the presidency and in another it's Obama! Everett's idea was far ahead of the prevailing physics, and was mostly ignored in its time.
Discouraged by his theory's lack of acceptance, Everett left academia for private industry. He later achieved financial success in the defence industry. In the 1970's the physics world finally took notice. One article appeared in Physics Today in 1970, and another in Analog magazine during 1977. Also in 1977 Wheeler invited Everett to give a talk at University of Texas in Austin, where Everett was treated like a star.
According to the documentary, Everett's life descended into depression and isolation. His death at age 51 was speeded by heavy smoking and drinking. His son Mark Everett is frontman for rock band the Eels. Many physicists today are fascinated by the many-worlds interpretation.
Disclaimer: The writer also came up with unusual ideas while in my twenties, but has not yet descended into smoke or drink. Stories like Everett's are easy to sympathise with. The idea of parallel world causes endless fascination for physics and science fiction.