- Robert Lowery
- Ken Morgan
- George Macready
- Prof. Ernst
- Ralph Morgan
- Professor Franklin Arnold
- Carole Mathews
- Babs Arnold
- Willie Best
- Flash
- Jack Ingram
- Dick Nordik
- Anthony Warde
- Joe Flint
- Ted Mapes
- Joe Butle
- Eddie Parker
- Blake
- Stanley Price
- Mead / Sam Nelson
- Charles King
- First Cop with Thor [Ch. 10,11,13] / Voice of Police Radio Dispatcher (Chs. 8, 15)
- Kenneth MacDonald
- Police Inspector Hamilton [Ch. 8,12]
- Bud Osborne
- Mason - Zoo Night Watchman [Ch. 3,8,10]
- Steve Benton
- Police Officer
- Ray Corrigan
- Thor the Gorilla
- Oliver Cross
- Reporter
- Dulce Day
- Reporter
- George Eldredge
- Professor Ames
- John Elliott
- Professor Marsden
- Dick Gordon
- Reporter
- Herschel Graham
- Reporter
- Kit Guard
- Zoo Guard
- Henry Hall
- Dr. John Draper
- Eddie Kane
- Dr. Draper's Assistant
- Forbes Murray
- Professor Jonathan Shaw
- Dick Rush
- McGarry - Armored Truck Guard
- Lee Shumway
- Tunnel Foreman Hartley
