Donald Gennaro was a lawyer sent by Cowan, Swain & Ross to inspect Jurassic Park. He was also the general counsel for InGen. He appears in both the book and film. Although he survives in the novel, in the film he was killed by the newly-escaped Tyrannosaurus rex. Both depictions of the character are extremely different in most regards.
Donald Gennaro was a lawyer who represented the investors of John Hammond's Jurassic Park. He is described in the script as:
DONALD GENNARO, forty, in a city man's idea of hiking clothes and a hundred dollar haircut...
Gennaro accompanied the endorsement team on a weekend trip to Jurassic Park to inspect the park's viability and security. Having his own reservations, informed Hammond "in 48 hours he'd shut him down"'. In turn Hammond responded "that in 48 hours he'd be accepting his apologies". After witnessing a real Brachiosaurus and watching a tour show Gennaro changed his views and believed Jurassic Park could make a fortune charging upwards of $2,000 to $10,000 a day. When Hammond states his intention for the park to be open to everyone and not just the super-rich, Gennaro off-handedly suggests having a "coupon day or something".
On the program tour Gennaro rides (like Ed Regis in the novel) in the same car as Hammond's grandkids Lex and Tim Murphy; he seems pretty okay having them there on the tour with him, unlike in the book where he is furious about the idea of having children there. They have two no-shows, one where they're supposed to see a Dilophosaurus but don't, and when they're supposed to see Rexy the T. rex eating a goat, the Tyrannosaurus doesn't appear at all. They also meet a sick female Triceratops.
With a storm coming the group headed back in the cars to the Visitor Center but the power was shut off by Dennis Nedry and the cars stopped in front of the Tyrannosaur Paddock where Gennaro, Lex, and Tim watched in horror as the T. rex ate the goat it was supposed to eat earlier. Gennaro runs out of the car and into a bathroom nearby and sits frightfully on a toilet, leaving Lex and Tim to fend for themselves from the T. rex. Ian Malcolm tried to distract the T. rex but only causes it to charge towards the bathroom. Gennaro starts reciting the "Hail Mary" prayer but quickly gives up and slams the stall door shut. This effort proves futile as the Tyrannosaurus smashes its head through the door and causes the entire structure to collapse around Gennaro. He attempts to stay still, but the rain causes him to rub his eyes, blowing his cover. The Tyrannosaurus then bites down on his upper-body, lifts him off the toilet and violently shakes him around, breaking his bones, tears him apart and eats him. When Muldoon and Ellie arrive at the Tyrannosaurus paddock in an attempt to look for survivors, they find his remains several feet apart.
In a deleted scene of The Lost World: Jurassic Park, 4 years after Gennaro's death, he is mentioned a few times. Peter Ludlow says that Gennaro's family sued InGen for 36.5 million dollars after his death.