Michael Sullivan is an original character mentioned in the Jurassic Park fanfiction Dinosaur Liberation Association.
Before Dinosaur Liberation Association
Michael, along with Erik Maximoff and Darren Sutter, was one of the top gentisicts on Isla Sorna. The three were chosen to create a hybrid dinosaur, but the experiment was abandoned due to the evacuation. Erik mentioned that he recieved an invitation to his wedding a year before.
In Canon Jurassic
Michael Sullivan was an InGen hunter in The Lost World: Jurassic Park, and was first named in Trespasser.