During the detonation of the Mutagen Bomb, Leonardo pushed his brothers to relative safety and took the brunt of the fallout himself. He was mutated into a gigantic, grotesque version of himself, and lost his memory of his life as Leonardo. Eventually, he became the warlord Maximus Kong, bent on conquering the apocalyptic world.
At some point, the Honey Badger Ravagers leader Verminator Rex came under his command. When Raphael took over the Ravagers and Scale Tail Clan after beating the leaders of the gangs, Verminator Rex ran to Maximus Kong and told him of the Red Stripe Army. Maximus Kong and Verminator Rex then set off to take Mira, the meerkat Mutant who had the map to the Oasis on her arm, so that he could control the legendary area or destroy it.
The Red Stripe Army fought Verminator Rex as well as Maximus Kong's Synthezoids. All of the Honey Badger Ravagers and Scale Tail Clan were wiped out, with the Scale Tail Clan's former leader Imperius Reptilicus squashed by Maximus Kong's own truck. Verminator Rex was taken out by Mira, and Raphael took the fight to the warlord himself.
Raphael managed to knock the helmet off of Maximus Kong, and realized that he was in fact his long assumed dead brother. Kong denied this, until he caught a vision of a young Raphael telling Leonardo that he loved him. Slowly, Leonardo began to regain his memories and recounted what happened on the day of the bomb.
Leonardo joined his brothers and the last of the Red Stripe Army and lived at the Oasis in happiness.
Leo had been double-mutated because of the mutagen bomb. His mutation enhanced his speed and strength, making him a fearsome foe for the other three Ninja Turtles.
- His outfit is based on Humungous from Mad Max 2: The Road Warrior.
- His design bears some resemblance to Leonardo's dark clone in the 2003 TV series' spin-off series, "Teenage Mutant Ninja Turtles: Fast Forward".