Leatherhead is a mutant American alligator and hot-headed ally of the Teenage Mutant Ninja Turtles. He was originally owned by a kind boy until his parents found out and flushed him down their bathroom toilet into the sewer. The Kraang found him, took him back to Dimension X and experimented on him, mutating him into an 8 ft. humanoid mutant alligator with a tough hide, uncontrollable force in his spirit, keen sense and superhuman strength. But since they were unable to break his spirit, Leatherhead eventually escaped through the portal that they used to travel to Earth. Stealing the power cell that powered the portal, he returned to the sewers and spent the next 6 months guarding the cell with a maze of booby traps, swearing to keep it away from the Kraang (so they wouldn't start their invasion) at the cost of his own life. He first appeared in "It Came From The Depths," where he was saved by Ninja Turtles from the Kraang when they were demanding the power cell's location. After being convinced by Michelangelo to take him back to their lair to be nursed back to health, the other three Turtles went out to find the power cell. Unfortunately, Leatherhead attacked them after finding out and went berserk, only to be kicked out of the lair by Splinter. Michelangelo, feeling sorry for his new friend, followed him back to his lair (with the other Turtles following), where Leatherhead explained the power cell's purpose and entrusted it into their hands as soon as the Kraang returned to demand it back. In "TCRI," after the Turtles lost the cell to the Kraang, they went to Leatherhead to ask for the portal's location, and in return, he helped them fight against Traag when the Kraang used the portal to bring him through. However, when they started using the portal to bring something else (possibly Granitor) through, Leatherhead sacrificed himself by entering the portal to stop it, dragging Traag with him. In "Into Dimension X," he was revealed to have survived the portal closing and has rapidly aged (due to the time difference between Earth and Dimension X). After sending a message to the Turtles through a Kraang communication orb warning them that the Kraang have perfected their mutagen, Michelangelo led a rescue mission for Leatherhead and together they stopped the Kraang from pouring the mutagen through the various portals while Donatello closed them all down, thus leaving one open for them to return to their own dimension. In "The Invasion," Leatherhead accompanied Splinter with finding the Turtles (who fled the lair when the Kraang invaded it) until they were cornered by Shredder , who seemingly killed him by slicing into his hide and sending falling into the river. In the two-part episode, "Battle for New York" Leatherhead was shown to have survived his wounds and recruited as second-in-command of the Mighty Mutanimals as they worked with the Turtles to take back the city from the Kraang.

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