The first version of this was called the AMU (Astronaut Maneuvering Unit) - unless the air force had a name that predated this. The Air Force
developed this in conjunction with the Gemini project.
Then it was renamed MMU (Manned Maneuvering Unit) and now it is called the EVU (Extravehicular Mobility Unit).
This looks to be a good starting point for researching the development history.
history.nasa.gov...