Nigel Jenkins is the perpetually nervous and all-around wimpy assistant of Dr. Eric Kiviat, who isn't much good for anything except his proficiency with a tranquilizer gun.
During the film's climactic assault on the soldiers' base camp by Cephu's tribe, Susan and George cut the ropes that have been keeping the female brontosaurus tied down for pretty much the entire third act. And now that she can stretch her legs, it's time for some righteous payback, and she proceeds to rampage through the camp, destroying everything in her path.
Attempting to halt her destructive tantrum, Nigel begins loading a tranquilizer gun. The dinosaur, ignoring him pretty much, walks right past him, but in doing so she knocks over some powerlines which fall onto Nigel, comically electrocuting him to death.