Some TMNT stuff was always meant for grownups.
"I let my rage consume me... I let my reptilian rage overwhelm my human intellect... ...and in my blind rage I have hurt other sentient beings..."
Leatherhead is an oft-ally of the Turtles that first appeared in Tales of the Teenage Mutant Ninja Turtles #6. Originally, Leatherhead was nothing more than an infant alligator that had escaped a robbery at a pet store, and found its way into the sewers. While in the sewers. Leatherhead was found by a pair of TCRI Utroms who decided to bring the creature to their headquarters. During his stay with the Utroms, Leatherhead was exposed to Mutagen, which caused him to mutate into a humanoid and intelligent being.
Living with the Utroms, Leatherhead ended up being separated from his "family" when the TCRI building self-destructed. The now homeless Leatherhead was forced to live in the sewers where a big-game hunter named Mr. Marlin continually attacked him. During one attack by the hunter, Leatherhead met the Turtles. Aiding Leatherhead in defeating the hunter, the Turtles decided to allow Leatherhead to live in their old home.
Eventually four Foot Clan ninjas encountered an eye-patch-wearing Leatherhead in the sewers. Fearing that Leatherhead would kill them, the ninjas tried to get on Leatherhead's good side by promising to aid him in creating his Transmat Device. Accepting the help, Leatherhead and the ninjas set to work creating the Transmat, only to be interrupted by the Turtles. After a brief skirmish, the Turtles learned that the Foot Soldiers were actually helping Leatherhead. Embarrassed by the incident the Turtles decided to aid the mutant alligator. Eventually the Transmat Device was complete; Leatherhead could finally reach the Utrom homeworld. Unfortunately, instead of teleporting Leatherhead, the device simply blew up in his face. This failure was too much for Leatherhead to handle and in a fit of rage, Leatherhead attacked his Foot assistants and vowed revenge on the Turtles, whom he blamed for wrecking his attempt to get "home."
Leatherhead later resurfaced in Volume 4. He makes an appearance at Master Splinter's funeral. He is then seen wrestling a mutated Raphael in the sewers before swimming off. It is unknown what his current relationship with the Turtles is, but Raphael's comment that he hopes he didn't hurt Leatherhead would make it seem as if they're at least on good terms.
He has also appeared in two issues of Tales of the TMNT Volume 2. In issue eight, a mentally unstable and delusional Leatherhead is discovered by Raphael to be building another Transmat Device. Leatherhead seems to harbor an insane grudge against Donatello, and nearly kills Raphael when he mistakes him for Donatello. Once the Transmat Device was finished, it suddenly kicked into operation and caused three Utroms to appear; these Utroms blast Leatherhead with a ray gun, and take him away, destroying the Transmat Device as they leave.
In issue twenty-three, the Turtles are recruited by the Utroms to save Leatherhead from a renegade group of Utrom radicals called "The Illuminated," the same ones who took him away in issue eight, in attempts to clone him into an army of mutants to aid in their world "cleansing" agenda. It is revealed that the Illuminated were secretly drugging Leatherhead, which caused him to subconsciously to build the second Transmat Device he was working on in issue eight, then wake up and remember little. It also caused his missing eye to heal and gave him a massive increase in size. The Turtles rescue Leatherhead, defeated the clones, and aided in the destruction of the Illuminated. Leatherhead returns to Earth with the turtles rather than going back to the Utrom home world. These events all take place between Volumes 2 and 4 of the Mirage series.
Brown returns to plot his creation after 19 years in the September 2007 issue of Tales of the TMNT. Out for a swim, Leatherhead encounters a group of aliens called Sigmurethites and attacks them. The alligator-man's Utrom guardian Dr. X also appears in this issue in a female scientist's exoskeleton.
- At several comic conventions, Leatherhead creator Ryan Brown has said he initially intended to kill the character off at the end of Tales of the Teenage Mutant Ninja Turtles Vol. 1, #6 by having the gator-man tumble into the underground gorge with the evil big game hunter but Turtle's creator Peter Laird nixed the idea opting to have Leatherhead survive and return to the sewers with the Turtles.
- Leatherhead shares his name with Leatherhead, a town in Surrey, England.
- Leatherhead is one of the few mutants originally mutated from a non-human (in any version of TMNT) who specifically identifies his own nature as (partially) human, as he does in "Triptyche". This is noteworthy considering Leatherhead was mutated intentionally by Utroms (unlike Splinter and the turtles), and raised by Utroms like another Utrom, and considers himself belonging to Utrom culture, and one might think it logical that as a mutant he would be gifted with an Utrom intellect like the people who raised him. Yet not only does he acknowledge his mutant side as being part human, but the rest of the series never mentions or shows him possessing any specifically Utrom biology or abilities.