There will be very heavy spoilers - do not read further if you haven't finished the novel.
Mr. World is the leader of the new gods, though his exact area of influence is left somewhat ambiguous in the novel. This may be an intentional decision, because
Mr. World is in fact Loki, and also Shadow's old cell mate, Low Key Lyesmith.
His appearance is somewhat distinctive:
Low Key, who was a grifter from Minnesota, smiled his scarred smile.
[. . .]
“How the hell should I know?” Lyesmith kept his orange-blond hair pretty much shaved. You could see the lines of his skull. “Tell you what, though. This country started going to hell when they stopped hanging folks. No gallows dirt. No gallows deals.”
Author's preferred text, chapter 1; emphasis mine.
The hair colour may be irrelevant, but combined with the scars on his face, which are faithful to a legend where his mouth was sewn shut after some incident or the other, I claim for this question that his appearance is very distinctive and recognisable.
There is also reason to believe that Loki had the same appearance when in his role as Mr. World:
He smiled then, his scarred smile. Mr. World was easily amused. Mr. Town had noticed this on several occasions. It had amused him to play chauffeur, in Kansas, after all.
Ibid, chapter 17; emphasis mine.
Now for my question - don't the new gods recognise that Mr. World is Loki? I realise this piece of trivia is not very well-known, especially with him being portrayed by such handsome actors lately, but surely the new gods have done their homeworks (with one of them literally being the god of wireless communication and all that) and must know the appearance of all the old gods ("know your enemy and know your ally" and all that).
Don't the new gods know that Mr. World is Loki, based on his appearance?
If they do, why on Earth would they accept him as their leader? Even if one factors in him being a Norse god and maybe having some sort of information about the enemy camp, he is the Trickster God - they should know this sword is of two ends.