John Hart
— Jack Armstrong
Rosemary La Planche
— Betty Fairfield
Claire James
— Princess Alura [Chs. 3-6, 9-11, 15]
Joe Brown Jr.
— Billy Fairfield (as Joe Brown)
Pierre Watkin
— Uncle Jim Fairfield
Wheeler Oakman
— Prof. Hobart Zorn
Jack Ingram
— Henchman Blair
Eddie Parker
— Henchman Slade
Hugh Prosser
— Vic Hardy