Baxter Stockman is a genius scientist working for the Foot Clan and Shredder. He is also a mutant fly, which does not seem to be particularly upsetting to him, though he does seem perturbed by the question of whether he is an employee or a hostage of the Foot Clan.
He was brought to Gotham in order to handle the construction of a mutagen-disseminating device for Ra's al Ghul. During this time, he was also in charge of the mutagen store that the Foot Clan had brought with them, as he was the one called upon to inject a League of Assassins ninja with it.
He finished the machine at the factory at Ace Chemicals, but the Turtles and Batman arrived before it could be launched. During the battle that ensued, Stockman was spotted by Robin, who challenged him to hand-to-hand combat. However, Stockman was terrified of the boy, pleading with him not to attack, then vomiting and fainting out of fear.
When the Ace Chemicals building began to explode and collapse, Stockman was last seen being dragged from the building by Robin.