"Beats me. I just think lasers are sick as Hell."
He first appeared in animated form in the 1987 TMNT series episode "Michelangelo Meets Mondo Gecko". He is voiced by Mariano in the 1987 series and by Robbie Rist in the 2012 series. Rist had previously voiced Michelangelo in the 1990 TMNT film trilogy, who is often portrayed as being a close friend of Mondo. In comics, Mondo Gecko appears in both the Archie series and the IDW series. In the comics and the 2012 series, he is a member of the Mighty Mutanimals, and is the only character to be apart of every incarnation of the team.
Mondo started his life as a human teenage boy playing in the local metal band "Merciless Slaughter", which alerted the Turtles as the noise came from Shredder's old hideout, who was in jail at the time. When the Turtles see the metal band practicing they decide to intervene as trespassing not only illegal, it is a bad idea, considering it was Shredder's territory and danger could be about. Sure enough, the band accidentally activate some dormant Foot Soldiers and are attacked. Mondo accidentally gets mutagen on him and because his latest contact was with his pet lizard he carried on his shoulders, his skin started turning green and his rear end sprouted a tail that ripped through his jeans, transforming him into an anthropomorphic gecko. His girlfriend, Candy Fine, decided to split up with him, and Mondo accepted, knowing she could not handle him as a mutant, and the two parted ways peacefully. Later, he became a member of the team known as the Mutanimals and eventually got back together with his girlfriend Candy.
After cancellation of the Mighty Mutanimals series, the Mutanimals received their own 7-part backup-series in the pages of Teenage Mutant Ninja Turtles Adventures beginning in issue 48 and ending in issue 54. This series saw the assassination of the Mutanimals at the hands of the high-tech Gang of Four. Issues 55-57 continued the aftermath of their death and its effect on the Turtles' storyline.
This version of Mondo made a brief appearance in All Tomorrow's Yesterdays.
In the IDW comics Mondo Gecko appears - along with Herman the Hermit Crab - as recruits for the foundation of a mutant army Old Hob selected in order to seize control of the streets of New York. As with the Archie series, Mondo uses a skateboard and quickly makes friends with Michelangelo. Mondo is a green lizard with blue eyebrows and black hair, he wears a yellow "Reptile Tendencies" shirt, ripped swagger jeans with chains, a watch on his right arm and what looks like sneakers cut open in the front.
The 2012 version of Mondo appears in the Amazing Adventures issue Cowa-Booyakasha, and is the same depiction as that of the TV series.
Mondo Gecko began his life as a normal lizard who fell into New York City sewers when the TMNT were mutated by the ooze, and he also became mutated. However, Mondo Gecko was picked up and carried away by Mr. X. One night, Michelangelo had a bad dream and woke up. When he heard noise up on the streets, he went up and met robbers. Among the robbers were Mondo Gecko, now a mutated and talking lizard who was raised by Mr. X. Mondo Gecko was now a member of a gang who worked for "Mr. X", the man who took Mondo away. Michelangelo convinced Mondo Gecko to turn on Mr. X. Together they fought Mr. X. After this, Mondo Gecko ends his career as a criminal and moves to the sewers and becomes "neighbors" with the TMNT and Splinter.
Mondo would return after being enlisted by the turtles to let himself get captured by Dirk Savage, a mutant hunter who had captured the likes of Tokka, Rahzar and the Punk Frogs, in order to find out where all the mutants were being taken to.
Jason, later named Mondo Gecko, is an ally to the Turtles and member of the Mighty Mutanimals.
Before the events of The Mutation Situation, Jason was a human boy living in New York City. Concurrent to the events of that episode (but not revealed until "Meet Mondo Gecko"), he was skateboarding a half-pipe on his building rooftop when he was hit by one of the many canisters of mutagen the turtles accidentally dropped from the sky. He had last touched his pet leopard gecko Lars, and thus became a mutant gecko himself. He was rejected by his parents and kicked out, becoming homeless. Jason was taken in as an errand boy by the criminal Xever Montes, who was called "Mr. X" by his underlings. While employed by Xever, Jason was exploited into committing petty crimes including theft.
Xever told Jason that the turtles were evil, and to help him capture them. In "Meet Mondo Gecko", Jason met and befriended Michelangelo and Casey Jones while all three of them were skateboarding on building rooftops. The moment Mikey saw Jason, he named him "Mondo Gecko," which quickly became Jason's nickname.
- Three action figures of Mondo have been made; a 1990 figure, a 1991 figure, and a 2015 figure.