I'm really curious about how they came into being like were they originally multiple entit...

I think its the later- thez got split after a traumatic event (like with DID)

I think Main Mugo is the fullest of the original and Geezer Mugo and Canine Mugo are smaller, less complex fragments of the original traumatized Hole Mugo. Geezer and Canine seem to be far less burdened by the memories that got them where they are. I imagine Canine Mugo probably represents the carnal hunger and instinct experienced by Hole Mugo and Geezer Mugo is the intellectual, manipulative part of Hole Mugo and was probably the main facilitator of the deal made with the family.

Did you mean "whole mugo"

I hope it’s the latter. It would be cool if it was multiple entities but too much drama. I’d prefer one with many inside Lmaoo