Jack Black as JB

Kyle Gass as KG

JR Reed as Lee

Ronnie James Dio as Dio

Paul F. Tompkins as Open Mic Host

Troy Gentile as Lil' JB

Ned Bellamy as Security Guard

Fred Armisen as Security Guard

Kirk Ward as Car Chase Cop / Gang Leader

Amy Poehler as Truck Stop Waitress

Tim Robbins as The Stranger

Dave Grohl as Satan

Ben Stiller as Guitar Center Guy

Lara Everly as Girl

Brittany Eldridge as Girl

Melissa-Anne Davenport as Girl

John Ennis as Gang Member

Vincent Foster as Gang Member

Jay Johnston as Gang Member

Colin Hanks as Drunk Frat Dude

Stephanie Erb as Al's Bar Waitress

Amy Adams as Gorgeous Woman

Milos Milicevic as Tattooed Biker

Molly Bryant as Ecstatic Woman

Michael Rivkin as Poopy Guy

Gregg Turkington as Stand Up Comic

Patrick M. Walsh as Exploding Head Guy

Bevin Kaye as Fainting Woman

Evie Peck as KG's Mother

Mason Knight as Young KG

Erik Walker as Bully

Cynthia Ettinger as Betty Black

Andrew Lewis Caldwell as Billy Black

Laura Milligan as Tarot Card Reader

Jason Segel as Frat Boy #1 (uncredited)

Meat Loaf as Bud Black (uncredited)

John C. Reilly as Sasquatch (uncredited)