Billy Clanton was a 19th century Human gunman who was involved in the shootout at the OK Corral on October 26th, 1881. Billy was one of three participants killed in the duel. His brother, Ike, survived.
In 2268, Montgomery Scott was identified as Billy Clanton in a bizzare recreation of the duel created by the Melkot. (TOS: "Spectre of the Gun")