A famous scientist invents a humanoid robot (the titular "monster"), so a greedy rival scientist plans to steal it for use in his criminal plans. His henchmen often kidnap a trained gorilla (the titular "ape") from the zoo, to aid in the schemes.
| Actor | Role |
|---|---|
 Robert LoweryKen Morgan | Ken Morgan |
 George MacreadyProf. Ernst | Prof. Ernst |
 Ralph MorganProf. Franklin Arnold | Prof. Franklin Arnold |
 Carole MathewsBabs Arnold | Babs Arnold |
 Willie BestFlash | Flash |
 Jack IngramDick Nordik | Dick Nordik |
 Anthony WardeJoe Flint | Joe Flint |
 Ted MapesJoe Butler | Joe Butler |
 Eddie ParkerBlake | Blake |
 Stanley PriceMead | Mead |
 Charles KingFirst Cop with Thor | First Cop with Thor |
 Kenneth MacDonaldPolice Inspector Hamilton | Police Inspector Hamilton |
 Bud OsborneMason | Mason |
 Ray CorriganThor | Thor |
 John ElliottProf. Marsden | Prof. Marsden |
 Kit GuardZoo Guard | Zoo Guard |