The Macellariusbloodline from Vampire: The Requiem. Their nickname is "Gluttons." Once someone's initiated into the bloodline, they gain up to 150 pounds in the next few nights. Oh, and the bloodline is made up mostly of cultured gourmands with a special taste for long pork.
The same gameline gives us the Formosae, "cousins" to the Kindred who feed on fat/ugliness and balloon up into horrifically disgusting monsters as their power increases. The general rule is that they are spiteful, disgusting, abusive monsters who love to prey on those who are insecure about their own weight and looks because it makes them feel better about their own morbidly obese frames.
In Dungeons & Dragons, amnizu, a type of powerful devil, are like this. Not only are they are obese and ugly, they act like snobbish arrogant, haughty bureaucrats, even towards devils weaker than themselves, whom they look down upon. The ones under the sway of Levistus, the Lord of the Fifth actually think that the laws of Hell don't apply to them (because Levistus told them that; of course, the same type of thinking got him in trouble).
Orcus has been depicted and described from his earliest appearances as obese to the point of rotundity. It's such a well-known trait of his that about half his most faithful servants become similarly fat. He is also the Demon Prince of Undeath, and widely regarded as one of the most despicable and irredeemable characters in the entire franchise.
Dominar Rasheth from Skorne Empire is one, deliberately going against the Proud Warrior Race code of his people and loving it.
In the Succession Wars era of BattleTech, the Draconis Combine's Dieron Military District Warlord, Vasily Cherenkoff, is notably overweight. Personality-wise, he is described in less than flattering terms as abrasive and barely competent, an intersection of a Glory SeekerMiles Gloriosus, The Neidermeyer, and Colonel Kilgore, feared and despised by his men, such that the leader of the Combine's Secret Police summed him up in disgust as a "fat fool." While he piloted a 100-ton Atlas, even that got him no respect, as his troops quietly joked it was the only 'Mech he fit in, and that the 'Mech's hips were giving out. He even went so far as to go rogue from his own government to pursue a war he thought they wanted but did not sanction. He eventually got what was coming to him.
Servants of Nurgle from Warhammer and Warhammer 40,000 are usually depicted as bloated, disease riddled bags of flesh. They see this as a good thing, as it helps them spread the "blessings" of Grandpa Nurgle to other races.
The Cone of Flesh from Midnight Circus takes the cake by being made of nothing but fat. More specifically, it's made up of all the assorted human and animal fats collecting in the fomorarch pits of the Seventh Generation, having attained sentience and coagulated into a nine-foot-tall pile of foul-smelling blubber. On top of being utterly revolting, the Cone is also a ready supporter of both the Wyrm and the Circus, and currently rules Freak City through brute force and low cunning; for good measure, it's in the habit of eating humans who make the mistake of overstaying their welcome, and might just have extended its appetites to any children trespassing on Freak territory.