Ewan McGregor

Rodney Copperbottom (voice)

Robin Williams

Fender (voice)

Halle Berry

Cappy (voice)

Amanda Bynes

Piper (voice)

Mel Brooks

Bigweld (voice)

Jim Broadbent

Madame Gasket (voice)

Greg Kinnear

Ratchet (voice)

Stanley Tucci

Herb Copperbottom (voice)

Dianne Wiest

Mrs. Copperbottom (voice)

Drew Carey

Crank (voice)

Harland Williams

Lug (voice)

Jennifer Coolidge

Aunt Fanny (voice)

Paul Giamatti

Tim the Gate Guard (voice)

Natasha Lyonne

Loretta Geargrinder (voice)

Chris Wedge

Wonderbot / Phone Booth (voice)

Dan Hedaya

Mr. Gunk (voice)

Marshall Efron

Lamppost / Toilet Bot / Bass Drum / Microphone

Terry Bradshaw

Broken Arm Bot (voice)

Al Roker

Mailbox (voice)

Lucille Bliss

Pigeon Lady (voice)

Jay Leno

Fire Hydrant (voice)

Lowell Ganz

Mr. Gasket (voice)

Paula Abdul

Watch (voice)

Jackie Hoffman

Water Cooler (voice)

Brian Scott McFadden

Trashcan Bot (voice)

Tim Nordquist

Tin Man (voice)

James Earl Jones

Voice Box at Hardware Store (voice)

Damien Fahey

Stage Announcer (voice)

Stephen Tobolowsky

Bigmouth Executive / Forge (voice)

Jansen Panettiere

Younger Rodney (voice)

Will Denton

Young Rodney (voice)

Crawford Wilson

Young Rodney (voice)

Jennifer Perito

Additional Voices

Alan Rosenberg

Jack Hammer (voice)

Lara Cody

Additional Voices

Cooper Cowgill

Additional Voices

Darin De Paul

Additional Voices

Dann Fink

Additional Voices

Ray Iannicelli

Additional Voices

Sondra James

Additional Voices

Vanessa Lemonides

Additional Voices

David Rossmer

Additional Voices

Chris Moyles

Stage Announcer (voice)

Chingy

DJ Robot (uncredited)

Sean Garnhart

Diesel (uncredited)

Paul Urmson

Diesel (uncredited)

Randy Jackson

Watch #2 (voice) (uncredited)

James Brown

Diesel (archive footage) (uncredited)