He is Corey's childhood friend whose real name is Austin. He's much smarter than the writers give him credit for as many suspect. Take a look at some YouTube's he's spoke on about himself, i.e. his tattoos'. He also owns several quite upscale vehicles that most would have a problem purchasing. Don't always judge a book by its cover. Good goin' Chum! :)
In Pawn Stars, Chumlee has no blood relation with the Rick's. He is Corey's devoted childhood friend and he's been around the shop since he was a kid. Rick actually treats him like his own son. Chumlee was given his nickname at age 12 by the father of a childhood friend, who named him after the walrus sidekick of Tennessee Tuxedo.