Charles the Fat*
Actually Karl der Gross
Actually loosely translated it could be Karl the Great
Personally I like the idea that he was unusually fat
He probably had more success with women than the other guy mentioned in that article, Alwin Clawecunt.
Don’t know if he/it had a first name but I’ve always liked “Slobberchops.”
Tryptophan The Tong Wielder
I have never heard that he was that fat; the estimate here is that he was between 5′ 10″ and 6′ 4″ and about 172 pounds.
Guess!
(Actually it comes from the Norse)
There is zero evidence that he was and that nickname is not even close to contemporary. History has not been kind to his reputation because he was in a sense one of history’s losers (not a massive one, really - but overall). But the usual view of him as being incompetent and lethargic appears likely to have come from a hostile monastic chronicle of his later reign in an area where he had imposed himself. Like all Carolingians he was a peripatetic ruler and seems to have been on the move frequently responding to various direct threats, hardly lethargic. His biggest failure was simply to produce an heir which would almost certainly have pre-empted his partial deposition, the higher nobility being fond of stability in troubled (viking) times. Had he done so his empire may have endured (at least for a little while) and a kinder assessment may have survived down the ages.
ETA: Though if you like big, fat kings there IS contemporary evidence that William the Conqueror aka William the Bastard was massively fat 
. It probably killed him when his belly came down hard on the pommel of his saddle and caused internal injuries while he was on campaign.
His eldest son Robert Curthose (“short stockings” - short and round, mockingly nicknamed by his unloving father) was also a chunky dude as very likely was Richard I Lionheart, at least by his end.
ETA II: Another one I like is that other Carolingian Charles the Bald. His nickname does seen to be contemporary, but there is no evidence he was bald. In fact one historian has pointed out that “reverse humor” was very common in that era, so he may in fact have been unusually hairy 
.
Indeed. Hence its placement in MPSIMS and not CS