- Don Terry
- Larry Kent
- Gwen Gaze
- Toni Morrell
- Walter Miller
- Carter 'The Shark' Collins
- Grant Withers
- Roderick Gridley
- George Rosener
- Capt. Samuel Cuttle
- Hobart Bosworth
- Dr. X
- Sandra Karina
- Nurse Zanya
- P.J. Kelly
- Prof. Gault
- Yakima Canutt
- Dreer (Mole-Men Leader)
- William Farnum
- George Brennan Westmore (Editor)
- Joe Caits
- Saltwater Jerry [Chs.1,4-7,13-15]
- Colin Campbell
- Hawkins (the Butler) [Chs. 1-3]
- Dave O'Brien
- Det. Jameson [Chs. 4-7]
- William Royle
- Paul Thorndyke [Ch.1]
- Warner Richmond
- Capt. Tom Stanton, alias Capt. Tom Faxton [Ch.1]
- Ted Adams
- Moore
- Harry Burns
- Pirate
- Louis Caits
- Henchman
- Ed Cassidy
- Passenger Ship Captain #2
- Willy Castello
- Pirate
- Eddie Foster
- Guard
- Jerry Frank
- Mole Men Rebel Leader
- Robert Frazer
- Passenger Ship Captain #1
- Joe Garcio
- Henchman
- Joseph W. Girard
- Newspaper Editor at Meeting
- Herman Hack
- Guard
- Frank Hagney
- Ambulance Driver
- Harry Harvey
- Toni's Kidnapper
- Reed Howes
- Pencil-Mustached Cortez Thug Leader
- Frank Lackteen
- Pedro
- Carl Mathews
- Fishing Captain
- Milburn Morante
- Bearded Pirate
- Jack Perrin
- Ambulance Attendant
- Josef Swickard
- Passenger Ship Doctor
- Robert Walker
- Dying Mole Man
- Blackie Whiteford
- Andy
- Roger Williams
- Guard
- Clara Kimball Young
- Cortez Hotel Maid
