Leatherhead is a mutant American Alligator that was used as lab rat by the Kraang.
Despite his monstrous form and appearance, Leatherhead has a surprisingly gentle soul and doesn't really wish to hurt anyone. He suffers from severe self-loathing from a life of horrific abuse and everybody around him fears him as a monster. He also has periodic bouts of rage in which he can lose complete control of himself which befits him as he is an alligator and he has taken a lot of abuse from the Kraang. When he awakens later, he is always contrite and regretful for the things he has done. Because of his horrific treatment by them, he has an everlasting hatred for the Kraang and simply hearing the word "Kraang" will throw him into a rage. So far, only Mikey has been able to calm him from these rages. Leatherhead has established a lair for himself in an abandoned subway car, where he keeps his few belongings; a stuffed crocodile, a record player with an old jazz record that he uses to calm his rage, and the Kraang power cell which he guards with his own life. He has proven to be a very strong ally to the Turtles, even saving them from Traag by throwing the rock monster and himself into the portal to Dimension X.
Leatherhead is a mutated alligator. He resembles a crocodilian with humanoid arms, legs, and the power to speak and reason. He is immensely large, has a long tail, sharp claws, and large mouth like all crocodilians do (long, narrow and V-shaped, teeth of upper and lower jaw showing when mouth closed). He has a tough, armored hide is extremely resistant to attacks, even from Kraang laser blasts. He possesses a third eyelid, which all crocodilians have so that they can see underwater. This third lid locks in place whenever Leatherhead goes into a rage. Later, he seems to be lighther in color due to age and has a scar across his left eye.
The Turtles, mainly Mikey, rescued Leatherhead when he was being chased by the Kraang. At first, excluding Mikey, they were wary about him because of his temper and size, but none the less, they see him as a valuable ally. Leatherhead sees them all as his only true friends that he can trust, and slowly starts opening up to them.
He is also a good friend with Master Splinter and helping finding the Turtles durign the invasion of the Kraang at New York.
From all of the enemies, he hates the Kraang most. The Foot Clan are also appear to be his enemies as well.
- He is a close friend with Mikey.
- He likes to grab Donnie's face and shake him when he's angry.
- When he is angry, Leatherhead's eyes are covered with white transparent nictating membranes that are naturally used as a third eylid to see underwater for alligators and crocodiles.
- He is the first member of the Mutanimals who had confronted Shredder.
- He likes old jazz music.