Steinbeck drew his inspiration for the work from his experience living and working as a "bindlestiff" - or itinerant farmhand - during the 1920s. In a 1937 interview in The New York Times, Steinbeck said that the character of Lennie was based on a mentally impaired man he met in his travels who was prone to episodes of uncontrollable rage. The central question of where or how such a man might fit into society drives the action of Of Mice and Men, and the rest of the characters in the book are developed largely in terms of their relationships to this enigmatic central figure. You can read more about Seinbeck at the GradeSaver link below: