Matthew Broderick
John Brown / Inspector Gadget / Robo Gadget
Rupert Everett
Sanford Scolex / Dr. Claw
Joely Fisher
Brenda / Robobrenda
René Auberjonois
Artemus Bradford
Richard Kiel
Famous Big Guy with Silver Teeth
Frances Bay
Thelma
Dabney Coleman
Chief Quimby
Mike Hagerty
Sikes
Mr. T
Himself
Andy Dick
Kramer
Michelle Trachtenberg
Penny
Brian George
Sore Guru
Cheri Oteri
Mayor Wilson
D.L. Hughley
Gadgetmobile (voice)
J.P. Manoux
Mayor's Sychophantic Assistant
Don Adams
Brain (voice)
Andy Heyward
Mr. D.I.C. - Party Guest