Most creators present what little we see of it as completely hideous but Jack Kirby who certainly created the look of Dr. Doom if not the entire character often said that Doom's face only had a small scar but his vanity caused him to hide it. So what can be said about that?
I'm going to avoid the authorship issues of the Lee/Kirby era of Marvel comics because that's a fight that would require a post of its own to cover. My personal opinion is that Lee had to sign off on the books as editor-in-chief and Kirby for all of dynamic art was churning out pages as a draftsman at that point so Kirby was unlikely to just turn in pages with a new character that Lee would appropriate. They were working close together as partners in those days and there would be give and take with Kirby having close hand in plotting. So my take is that the stories in these very early Fantastic Four issues that I'm going to reference were mainly Lee with Kirby's input. Kirby's creative control would increase as Lee and Kirby continued to work together until that golden year of 1966 where they synchronized perfectly.
Okay, back to Doom. Here is his origin as given in his first appearance:
We start to see a little more depth in Fantastic Four Annual #2:
There's several important things on these pages. First, the glimpse of his head that we get when he's smashing the mirror isn't bald and scarred. Could Kirby's choice of how to depict Doom have changed?
Also note that Doom immediately puts on a metal mask lifted out of a smoking urn. It's still burning when they put it on his face. That will be important in a moment.
So from this point on Doom's origin is pretty much set and this version is what we see. Kirby left Marvel comics in 1970 and sometime after that the story starts circulating from convention appearances that Doom isn't badly scarred at all, he just has one mark on his face. While it's possible Kirby started saying this before leaving Marvel comics the earliest reference I have been able to find is the early seventies which is when he was working for DC comics. Kirby did a few sketches like this of Doom without his mask:

Finally, the second biggest question about Dr. Doom is what exactly is his doctorate in? As we've just seen repeatedly he was kicked out of college before getting it so did he go through a Guatemalan diploma mill? That was officially answered a few weeks ago: Doom lies about his credentials. For shame, "Doctor" Doom, is there no end to your villainy?