In "License to Till", Mertz makes an appearance by showing up at a party, and is shown praising Steve, when he offers to drive members of the party to another party across town.
He tricks Steve and his friends into coming to one of his parties for the cool kids in "The Unincludeds", there they are egged. When they become prosperous in the future and invent a time machine, he steals one and returns to the past where he plants the idea for them to throw a party while posing as a janitor, which results in them becoming popular and ruining their future.
In "Mean Francine", it is revealed that he is an orphan adopted by his abusive uncle for monetary purposes and he is beaten regularly by a wrench.
Mertz is voiced by Judah Miller.
- "License to Till"
- "The Scarlett Getter"
- "Steve and Snot's Test-Tubular Adventure"
- "Scents and Sensei-bility"
- "The Unincludeds"
- "The Nova Centauris-Burgh Board Of Tourism Presents: American Dad"
- "Criss-Cross Applesauce: The Ballad Of Billy Jesusworth"
- "The Witches of Langley"
- "My Purity Ball and Chain"
- "Mean Francine"