Gareth Grimes is a character that appeared in Diary of a Wimpy Kid: Old School. He is one of Greg's cabinmates that stayed at Hardscrabble Farms for a week. During the trust fall activity, Rowley and Gareth held each other's arm in order to catch Jeffrey Swanson. When Jeffrey landed, Gareth's and Rowley's arms collapsed, causing Gareth and Rowley to bang their heads. Gareth lost a tooth, which Emilio Mendoza found in Rowley's forehead. The nurse came to stop the bleeding and to check the injury, but the tooth could not be removed. Later, Rowley goes to the emergency room, and comes back a few days later with Gareth's tooth in a jar.
- Diary of a Wimpy Kid: Old School (First and only appearance)