Donald Gennaro represnets the law firm Cowan, Swain & Ross and goes on the park tour with Alan Grant, Ellie Sattler, Ian Malcolm and Hammond's grandchildren Tim and Lex. Gennaro opts to remain with Ellie while she tends to a sick stegosaurus along with Dr. Harding, and thus he is absent when the Tyrannosaurus rex breaks free from her paddock. Later, he becomes trapped in a truck that is parked inside of the resort's generator shed and is attacked by a Velociraptor, but rescued by Grant. He then joins him and Ellie in venturing down into the raptor nest to see how raptors have bred, and following this makes it off the island alive when the Costa Rican military arrives to eradicate the dinosaurs. He later dies of dysentery however.
Gennaro was the representing InGen's investors. Gennaro was dispatched to look into the affair at Jurassic Park following the accident involving the death of a worker. His employers wanted John Hammond to get experts to sign off on the island, and Gennaro was sent to get Ian Malcolm. They thought he was "too trendy," but decided to have him come along anyway.
Gennaro had no idea what was being done on Isla Nublar. Upon arriving, he was stunned by the sight of a real-live brachiosaurus. Before, he was skeptical of Jurassic Park's future, but after seeing the dinosaurs he became certain they could make a fortune with it. Gennaro wanted to make it so they charge up to $2,000 or $10,000 a day for visitors. However, Hammond made him back down by saying that everyone in the world had the right to see the dinosaurs, not just the super-rich.
Gennaro went on the tour with Doctors Alan Grant, Ellie Sattler and Malcolm and Hammond's grandchildren Tim and Lex. When the tyrannosaur escaped its paddock, Gennaro abandoned the kids in a fit of wild panic, hiding in a nearby outhouse. This did not save him for long, though. While chasing Malcolm, the tyrannosaur knocked over Gennaro's hiding place. Taking one look at the lawyer, the dinosaur quickly gobbled him up off the toilet he was crouched on.