This character has done phenomenally well for himself considering his very obscure start.
He was first published by Ace Magazines (a defunct Golden Age company) in Lightning Comics 6, April 1941 appearing until 1943 (If anyone collects Project: Superpowers this is the same company that Lightning, the Sword and the non Quality comics Magno appeared in)
Revived in 1993 to be a bad guy (Dr Death) in an Invaders mini series along with several other public domain non Marvel Golden Age characters, he was tied to the origin of the Golden Age Human Torch, giving him a solid Marvel connection ... if he hadn't been killed of that is!
But somebody liked him as it was revealed he'd survived and he was brought into the X Men franchise. So as a co creator of the Torch and part of the X World, the Doc is the ultimate success story considering he wasn't even a Marvel character to start with and he's survived one attempt to kill him off!
So for anyone reading this - did you first encounter the character through the X Men and did it encourage you to seek out Golden Age stuff like the 1993 Invaders mini etc because of it or are you someone who was into the Golden Age and bought X Men because of Dr Nemesis?
Personally i'm into both so i found it very cool to see an old Golden Ager i'd previously thought dead and gone, return in the X part of the MU