Mr. Kidd is a rival kid teacher at Finnegan High, and Echo's former interest. Unlike Adam, he made a very good first impression on everyone else in the school, and Principal Tater likes him, thinking he is the only kid teacher in the school. He is the main antagonist in the episode of the same name.
Role in the show
When it was discovered Adam and Echo where dating, the school board accepted it, so long as Echo is taught by another science teacher. As it happens, Echo's memories were erassed by Preston Pickles, and Mr. Kidd makes a good impression on her.
He also makes the same impression on the other students, despite teaching the same stuff as Adam. When Adam tries to restore Echo's memories, Kidd offers to help but alters the machine enough to make Echo think she and Kidd are dating. To add insult to injury, Kidd steals everyones memories of Adam and replaces those memories with him, including his own mother. Kidd reveals to Adam that he intends to steal Adam's life, and has Adam's mother kick him out of his home.
Adam tries to steal the memory machine from the class but is confronted by Derby. It turns out Derby remembers the times Adam was a jerk, but only as Kidd. Developing a hatred for Kidd, Derby teams up with Adam. Adam disguises himself as a salesmen to sell hats linked to the memory machine, but the plan is foiled by Kidd. Ironically, Kidd's own plan was foiled when Adam ends up kissing Echo, getting her memory back. She reveals that Kidd tricked them, and eventually gets everyone's memories back.
In the last scene, Kidd is seen packing up, having been fired. Since Adam's mother didn't get her memories back, she still thinks Kidd is her son, and grounds him for not doing chores.