|~ Leatherhead's catchphrase in the original cartoon.|
In the 1987 cartoon, he is a mutated villain who made slaves out of the Punk Frogs until he was captured by the Teenage Mutant Ninja Turtles who came to save the frogs. He escaped thanks to Shredder, Rocksteady, and Bebop. Then he went to New York City to get revenge on the turtles, but got captured by the Rat King, and later freed himself and he tried to wrestle him down until they made an alliance to capture the turtles and send robot-rats and android alligators to kill them, however this failed and they later worked together again along with some other villains one time with Shredder to capture them.
In the 2003 animated series, Leatherhead has a different backstory: He was once a baby alligator that got mutated. He was found by an alien race called the Utroms and became their top scientist. Later, he went wild and escaped. He was then found by the Turtles to be an ally. There are two sides of his personality, a brilliant being and a wild monster.
Leatherhead started life as a baby alligator who had been secretly raised by a child. But the child's parents found him, and flushed him down the toilet. He ended up being banished to the sewer drains, where he was found by the Kraangs. The Kraang, upon discovering him, took him in and subjected him to several tests. But he escaped and revolted against the Kraangs. The turtles saved him, but the damage had already been done. His hatred runs so deep that even hearing the word 'Kraang' sends him into an uncontrollable rage. Later he became a valuable ally to the Turtles.