Who are Kreatz and Mauk?
They're characters from the Metroid manga (shown here beside my versions of them)
Kreatz is the little smug one and Mauk is the one who isn't Kreatz. They're part of the broader Galactic Federation - the games don't focus on the non-human factions these days (maybe Prime 4 does but I haven't played it yet). I like the two of them as a connection to the GF for Samus that doesn't directly involve interacting with humans, like a sort of protective 'barrier' for her. Of course there is also Malkovich and Higgs etc but there's more emotional baggage with that side of things.
In the manga these two take some part in the mission to Zebes. I prefer that it's a lone mission for Samus but I still think they're cool characters in the broader lore.