Leatherhead is the turtle-like mutant who allies with the Teenage Mutant Ninja Turtles and first appeared in 1988.
Leatherhead is generally depicted as a mutant alligator rather than a member of the four-turtle team. Depending on the continuity, he may be an ally, a dangerous rival, or a character whose intelligence and loyalties are manipulated by villains. His size and strength make him visually distinct from the brothers.
The character first appeared in the Mirage comic in 1988 and was later adapted into the animated series and other media. Different versions change his personality, origin, and relationship with the turtles.
Leatherhead is often confused with Tokka, a mutant snapping turtle introduced in the second live-action film, or with Slash, another mutant turtle. Those are separate characters.