Underdog

Jason Lee

Shoeshine / Underdog (voice)

Peter Dinklage

Dr. Simon Barsinister

Jim Belushi

Dan Unger

Patrick Warburton

Cad

Alex Neuberger

Jack Unger

Taylor Momsen

Molly

John Slattery

Mayor

Amy Adams

Polly Purebred (voice)

Brad Garrett

Riff Raff (voice)

Samantha Bee

Principal

Timothy Crowe

Police Chief

Larry Vigus

Security Guard

Mario Mariani

Police Officer

Bates Wilder

Cop

Alexander 'Alex' Garde

Small Boy

Christopher Francis Byrnes

Mailman (as Christopher Byrnes)