Dead givaway for the German origin: one of the mutants supporting our hero early on is a German sci fi writer named Ernst Ellert from Munich. :) (Kidding, though I really can't see a US sci fi series in the 1960s making one of the mutants a German sci fi writer.) (The other mutants are mainly Japanese - since Scheer & Darlton went with the "Hiroshima caused mutants to be born" thing very en vogue in 1960s sci fi), but also African, Australian, Russian; there are only two Americans in the first mutant group, and neither of them a prominent character.)

Mind you, given the "astronaut makes it to the moon, discovers stranded aliens" premise of the first issue, he simply could not have been other than either American or Russian. Though later continuity gave him a German granddad on the maternal side.