Dr. McCoy's first name in Star Trek: The Original Series is Leonard.
Leonard Horatio McCoy, played by DeForest Kelley, is the USS Enterprise's chief medical officer and one of Captain Kirk's two closest friends. His nickname, “Bones,” reflects his medical role and became one of the series' most recognizable character names.
McCoy often represents compassion and instinct in the show's central trio. Kirk makes practical command decisions, Spock emphasizes logic, and McCoy argues for the human and ethical consequences. Their disagreements provide much of the series' dramatic and comic energy, but McCoy remains a trusted physician and officer.
A common mix-up is confusing McCoy's first name with those of other Enterprise crew members. Leonard is also notable because Spock later places his katra, or living essence, in McCoy in Star Trek III: The Search for Spock. Kelley reprised the role in the original Star Trek films and in the 2009 reboot, where Karl Urban played an alternate-timeline version.