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 time as Leonardo. Eventually, he became the warlord Maximus Kong and traveled the wasteland in a massive truck.
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 they could control the legendary area themselves.
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 Raphael as he was before the Mutagen Bomb, telling him that he loved him. Slowly, Leonardo began to regain his memories and recounted what happened on the day of the bomb. He got double mutated and turn into a monster.
Leonardo joined his brothers and the last of the Red Stripe Army and lived at the Oasis in happiness.
Leonardo 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 Turtles.
- His outfit is based on Mr. Humungous from Mad Max 2: The Road Warrior.