I happened to be paging through the early issues of the Golden Age Captain America, when I came to issue #14 (1942), and found myself face to face with-- The Yellow Claw!
But he had nothing to do with the 1950s character, whom Steranko and others revived for Marvel Comics, much less anything to do with the 1915 Sax Rohmer novel of that title.
Here's the first "Marvel" Yellow Claw:
He's got no backstory, though he makes one remark about Americans, so presumably he's not one. He's just a weird masked dude who kills people with poisoned flowers, and who is brought to heel by Captain America and Bucky.
And that's about all there is to say about him!