In his first appearance, he was seen at the Simpsons' pool with the other kids. He asked Lisa if she wanted to go with his family for a weekend in the country.
He further explained they would be doing various activities. Lisa agreed to go with him, but when all the children left the Simpsons' pool for Martin's pool, it's likely Rex reconsidered his offer to Lisa.
In "Bart vs. Lisa vs. the Third Grade", Rex appeared on the field trip with the other children in Mrs. McConnell's third grade class. His partner for the field trip was a girl. He was later seen in Mrs. McConnell's fourth grade class in Stealing First Base.
Rex appears to be intellectually equal to Lisa as shown in "Bart of Darkness". Rex is usually seen around the school as a secondary character with the other children. He's only been seen in his class once and has not had a role since "Bart of Darkness".
Rex was first seen with a pale or white skin complexion. His skin complexion has changed to brown or yellow as the show progressed. He normally wears a white shirt, a green sweater, long brown pants, and brown shoes.
He has light brown or regular brown hair and wears glasses sometimes. In some recent episodes, he has been seen with brown skin.
- His name wasn't revealed in the show, but looking at SNPP, his name is listed as Rex.
- In some episodes, Rex isn't seen wearing glasses.