What, no one's mentioned Baron Blood yet? He goes way back to the Big One with Red Skull. I have seen some other great ideas here though. Degaton, Savage and Ultrahumanite would all go nicely.

Edit: and Arnim Zola of course.

Hey, now. If the Red Skull wants to occassionally give Baron Blood "The Big One", it's between them. Afterall, they're both consenting adults. And, in New York, they can now legally marry so the Red Skull can slip the Big One to Baron Blood more often and not be frowned upon by society.


And while Baron Blood was around in World War One, the Red Skull was not.

And then I found:

(cue drum roll)

Dark Beast!! Would he serve as a 'mad scientist' for Red Skull? How unscrupulous is he? Sadly, I don't know much about the character...