I recently watched Robot Monster on YouTube and wow... It was bad, but at least I liked the monster's design despite the cheapness of it all, it was initially intended to look completely robotic but due to budgetary reasons, director Phil Tucker got his friend George Barrows to play the lead monster with a gorilla suit he already had made and stuck a diving helmet atop of it. Barrows later used this same gorilla suit to play gorillas in film and TV and the suit was borrowed from him in the 1961 film Konga.
Ro-Man as seen in Robot Monster.
The gorilla suit made and used by Barrows throughout most of his career, the suit is currently on display at Natural History Museum of Los Angeles County.
Here's Robot Monster in case any of you want to see it, it appears the film is in the public domain since there's no copyright protection over it.
https://www.youtube.com/watch?v=DqV2RQCtSf8&t