As in Stephen Malkmus, of the band Pavement.
I’ve read of other people with this name, sometimes spelled Malchemus.
Is it Greek?
Maybe Machelmus: I think it’s one of those Latin-sounding names that made it into Dutch, and, looking at Google, seems to go very very far back in Utrecht.
A quick internet search of genealogy sites suggests that the American Malkmus clan comes from Germany, esp. Hesse. That would jibe with capybara’s logical suggestion.