|Relatives||Marshall (brother), unnamed mother|
|Introduced In||"USG and ESB"|
HatBoy is a long, cone-shaped, fuzzy hat who is olive green in color with blue tassels and a blue lining on his bottom. He has no eyes or nose, and just a mouth. He works like a normal hat, often perching on people's heads.
HatBoy was introduced in the first episode when he helped ESB find somewhere to eat. He is nice and fun-loving, and often hangs out with ESB. He is the squares' main sidekick, helping them out in almost all of his quests. He also has a crush on Tammi, the princess Hat.