>>114889177His supporting cast usually boils down to
>Dr Erdel (depending on if he lives or not after their first encounter)>M'gaan>Jemm>Some lady cop/assistant to John JonesWhich is a perfectly serviceable number for his usual stories if I'm going to be honest.
If we're going to include rogues, then there are some recurring villains like the white martians, white saturnians, Malefic, Shaggy Man, and Despero. His Ostrander run included some really great villains like Headmaster, Cabal and Bette Noir. His silver age stories also has some characters like General Blanx and Mister V who, with some pretty easy retooling, can be pretty engaging villains as well.
Of course, the issue with MM is that almost every new run entails a complete revamp to his origins, cast, overarching story and even characterization, meaning that there's not much of a consistent or well-developed mythos for writers to pull upon, so they just ending up making new stuff. Which is a shame because there's plenty of stuff there, they often just don't use it or build upon it in meaningful ways.