John Cusack

Igor (voice)

Myleene Klass

Dr. Holzwurm (voice)

Robin Walsh

Dr. Holzwurm's Igor (voice)

John Cleese

Dr. Glickenstein (voice)

Steve Buscemi

Scamper (voice)

Sean Hayes

Brain (voice)

Eddie Izzard

Dr. Schadenfreude (voice)

Jay Leno

King Malbert (voice)

Jennifer Coolidge

Jaclyn / Heidi (voice)

Molly Shannon

Eva (voice)

James Lipton

Himself

Christian Slater

Dr. Schadenfreude's Igor (voice)

Arsenio Hall

Carl Cristall (voice)

Jess Harnell

Announcer / Royal Guard #2 (voice)

Paul Vogt

Buzz Offmann (voice)

Frank Welker

Animals' vocal effects (voice) (uncredited)