Fritz Reuter Leiber Jr. (/ ˈ l aɪ b ər / LEYE-bər; December 24, 1910 – September 5, 1992) was an American writer of fantasy, horror, and science fiction. He was also a poet, actor in theater and films, playwright, and chess expert. With writers such as Robert E. Howard and Michael Moorcock, Leiber is one of the fathers of sword and sorcery and coined the term.

Fritz originated as a German nickname for Friedrich, or Frederick (Der Alte Fritz, and Stary Fryc were common nicknames for King Frederick II of Prussia and Frederick III, German Emperor) as well as for similar names including Fridolin and, less commonly, Francis.Fritz (Fryc) was also a name given to German troops by the Entente powers equivalent to the derogative Tommy.