Reptar is a fictional character that the gang used to love when they were babies. Reptar clearly lost his popularity in All Grown Up!
Reptar only made 1 appearance in All Grown Up!, in the episode "The Curse of Reptar" in which the family buys a new pool, and during construction the gang's old Reptar toy is found (as Spike buried him years ago) and the gang throws him away. A horrible series of events happen leading them to think they angered Reptar, so they get him out of the dump, and bury him. Later Tommy secretly goes outside and puts Reptar under his bed. Reptar also appeared on Tommy's watch in a few episodes.