T-Rex or Tyrannosaurus, is the child from the cool family.
Bart and Lisa met him when they were invited into 740 Evergreen Terrace. They were surprised to see all the obscure things that T-Rex had in his room and were even more shocked to find that he didn't own a TV.
At T-Rex's birthday party, T-Rex mocked the present that Homer had made for him (a jacket with Dino-Cool written in the back along with a dinosaur drawing), and mocked Homer. Bart stood up for his father and attacked T-Rex, leading into a fight. This fight is what made the two families stop being friends. His rude behavior caused Bart to fight him after T-Rex insults Homer.
Later, after Bart and T-Rex had forgiven each other, Bart asked T-Rex if he wanted to come to his to watch The Krusty the Clown Show. T-Rex said that he had to stir compost but Bart persuaded him to leave it. The compost started to burn and set fire to the Devil Donuts truck. After this, T-Rex and his family left Springfield.
T-Rex seems to be nasty around his friends, as seen when he mocked Homer. However, he doesn't seem to hold grudges for long and knows when he is in the wrong and accepts it.
He appears negatively effected by his family's trendy lifestyle. He doesn't get a lot of sleep because of the cool activities he goes to, causing him to be nasty and short with people.
He craves regular kid activities, as he was excited at the idea of watching normal TV with commercials and wanted to go eat fast food with Bart.
- T-Rex is shown to be a supporter of English football club West Ham United as there are banners of the team in his bedroom. However, the banner is not in West Ham's colors of claret and sky blue, instead being in yellow and green.
- It is also possible that T-Rex is left-handed judging by the bass guitar neck behind him in one scene.
- He is only allowed to watch what his father has on his tablet.
- The inscription on the jacket that Homer gave him is a pun on his name.