Mr. Big is a gangster in the episode Raphael Drives 'Em Wild of the 1987 animated series. He is approximately the size of a small child, which does not seem to be an issue for him except when directly applicable.
When the Premier of Vadeem visited New York, Mr. Big concocted a simple scheme to get control of his oil shares: he would kidnap the Premier and switch his brain with that of Mr. Big's minion Little Huey, using the Transmogrifier. Little Huey would then sign the oil over to Mr. Big. However, the scheme was disrupted when the Transmogrifier was lost in a cab.
Mr. Big and Little Huey set out to reclaim the device, unaware that it was building up to a detonation. Upon finding it in Oscar's cab, they then went to kidnap the Premier and take him to their dockside hideout. However, when Mr. Big turned on Oscar (who was then in Raphael's body), he easily defeated them, forcing Mr. Big to pursue the cab with the Premier inside.
This chase ultimately led to a four-way collision with the cab, the Turtle Van and the news van. Mr. Big became trapped in his car, and was left there by the Turtles until the police could arrive.