"I White" vs "I Black"

Stephan Zweig in his "Schachnovelle" (or "Chess Story" or "The Royal Game" as it has been translated in english) tells the story of an Austrian lawyer captured by the Nazis and subjected to a torture depriving him of all stimuli. He manages to maintain his sanity only through the theft of a book of past masters' chess games which he plays endlessly, voraciously learning each one until they overwhelm his imagination to such an extent that he becomes consumed by chess. He starts playing chess against himself, splitting his personality into an "I White" and "I Black" chess player in an effort to ward off insanity.

Bobby Fischer, the great American Chess player also played chess against himself when he was a child. "Eventually, I would checkmate the other guy", he joked later in life.