The computer-system analyst at Jurassic Park, Dennis Nedry fills the role of disgruntled employee. He's described as overweight and as a slob, and that kind of sums up a lot about him.
Now, what actually happens is this: Nedry is annoyed at the blame he's received for the bugs in the park's computer system. His frustration is somewhat warranted: he was kept in the dark about the purpose of the system and had to put it together without all the information he needed. John Hammond's overconfidence strikes again: not only could Nedry not make the system perfect, he also turns against his employer and tries to help out the competition.
Yeah, Nedry basically chooses to smuggle dinosaur embryos out of the park and sell them to a competitor. He pays the price, though: he's killed in the act—and pretty gruesomely at that.