Renault Renaldo Duncan, better known as Duncan Renaldo, was a Romanian-born American actor best remembered for his portrayal of The Cisco Kid in films and on the 1950–1956 American TV series The Cisco Kid.

The Cisco Kid is a fictional character found in numerous film, radio, television and comic book series based on the fictional Western character created by O. Henry in his 1907 short story "The Caballero's Way", published in Everybody's Magazine, v17, July 1907, as well as in the collection Heart of the West (1907). Originally a murderous criminal in O. Henry's story, the Kid was depicted as a heroic Mexican caballero later in films, radio and television adaptations.