Kelley's first broadcast appearance as Doctor Leonard McCoy was in "The Man Trap" (1966). Despite his character's prominence, Kelley's contract granted him only a "featuring" credit; it was not until the second season that he was given "starring" credit, at the urging of producer Robert Justman. Kelley was apprehensive about "Star Trek"s future, telling Roddenberry that the show was "going to be the biggest hit or the biggest miss God ever made". Kelley portrayed McCoy throughout the original "Star Trek" series and voiced the character in the animated "Star Trek".