The Tyrannosaurus Rex, or T-Rex for short, is the main antagonist of the 1978 film Planet of Dinosaurs. He is an extraterrestrial dinosaur living on a planet where the inhabitants evolved to resemble prehistoric dinosaurs from Earth, through convergent evolution.
His vocal sound effects were provided by Darrell Cotton.
He first appeared walking behind a hill in front of the humans. They run off and the Tyrannosaurus fights a Stegosaurus and kills him after a brief fight.
He 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 him. They go back to their cave, realizing that 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 him 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 an alien that resembles a smaller version of the infamous Rhedosaurus, which the T-Rex kills and brings him to his cave. When the stakes are prepared to penetrate the T-Rex, the group taunt the T-Rex outside of his cave and provoked him 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 to death, finally killing him for good.
The alien T-Rex was a vicious, misanthropic, greedy, and a very determined creature. Unlike the real-life Tyrannosaurs that roamed the Earth, he was more than willing to kill dinosaurs and leave the body, suggesting that he killed for sport ( similar to the Indominus Rex from the Jurassic Park franchise). He had traces of cunning, knowing to avoid poisoned carrion, surprise human prey, yet was stupid enough to impale himself.
- The fact about the T-Rex was an alien that just happen to look just like a dinosaur from Earth is a wink to the fact. Many aliens in popular culture look extremely human.
- The T-Rex preyed upon a downsized Rhedosaurus, a fictional species that also appeared in the movie, "The Beast from 20,000 Fathoms". But in that movie, he was ironically enormous and big enough to have a fight with the Tyrannosaurus, but failed to defeat him, because the T-Rex won.
- He lacked feathers, walked with a vertical stance, had zombie hands and had a wiggly tail it dragged, unlike Earth T-Rexes. This reflects older ideas about how the Tyrannosaurus looked, moved, and acted in the movie.