Role in the Film
He first appeared walking behind a hill in front of the humans. They run off and the Tyrannosaurus fights a Stegosaurus and kills it after a brief fight.
It followed the humans up the mountain and killed the Allosaurus the humans had intended on killing. He leaves a footprint and when the humans find it, they go back to their cave, realizing the T-Rex has followed them. The commander, Lee, reassured the group that the T-Rex could not follow them.
The T-Rex proved Lee wrong when he attacked the humans at night and killing Derna when she tries to get the laser to fight off the giant. Her death prompts one of the humans, Jim, to try to kill the dinosaur.
They first try to poison him by smearing poisonous berries on a dead Polacanthus for the T-Rex to eat. The plan backfires when the T-Rex shows up behind the group and kills Mike when he tries to fight it off.
Jim then comes up with the idea to impale the T-Rex on several wooden stakes. The T-Rex comes out to hunt before the humans can prepare the stakes but Lee leads him to a Rhedosaurus, which the T-Rex kills and brings to his cave. When the stakes are prepared, the group taunt the T-Rex outside it's cave and provoke it into chasing them. The T-Rex was so eager to catch the humans that he did not notice the stakes in front of him and ran right into them, impaling him and finally killing him.