In Stephen King's Bag of Bones, custody lawyer Elmer Durgin is a Fat Bastard. He is also a lawyer, but main character Michael Noonan speculates that Durgin's physical appearance is responsible for his repugnant personality rather than his profession, identifying Durgin as a member of a sub-species he calls "Evil Little Fat Folks/Fucks". Noonan says that most fat people are generally nice, but the Evil Little Fat Folks are naturally hateful (especially toward people who are physically fit) and bent on world domination.
Billy Bunter of Greyfriars has got to be one of the archetypes for this trope, having made his first appearance in 1908 and becoming so well-known that his name was long used in the UK as an insult for real life Fat Bastards. Comically greedy, snobbish, dishonest, inept, self-centred, lazy, stupid, mean, cowardly and always, always on the scrounge, he provided the perfect foil for his upright and honest classmates and became so popular that he eventually took on the title role for the series.
Dennis Nedry from Jurassic Park. Arnold even refers to him as such.
The male Dursleys, particularly Dudley. Indeed, in Dudley's introductions in the first book, Rowling spends nearly as much time going over how fat he is as she does over his actual bullying of Harry.
Rowling did eventually apparently become uncomfortable with how she was using this trope to equate evil with being overweight, and eventually gave Dudley enough physical training for him to be a competent boxer (though he's still "vast as ever"). Then in the last book Dudley turns out to be halfway decent at the last second, and is merely described as "muscular."
Peter Pettigrew, evil murderous traitor extraordinaire, is described as having been fat or 'chubby' in his youth, though when they first see him as an adult he has the look of 'having lost a great deal of weight in a short amount of time' which is equally unflattering.
Umbridge is described as squat and toadlike.
Terry Pratchett lampshades this in Going Postal, where one of the chairmen at the Grand Trunks Company is described as fat, multi-chinned and having a grating voice and an expression like a piglet, and a footnote says that it's stereotypical to say that someone like that couldn't be a kind and generous man, like it's stereotypical to say a man in a striped shirt coming in through your window in the middle of the night is a burglar.
Matilda's mother is a female version. Her father is this in the movie. The Trunchbull is another female version.
That's got to be justified. The man weighed 200 kilograms (441 pounds) but could only support 1/4 of that by muscle-power without anti-gravity suspensors. While there are certainly active people who reach that weight, they also develop the body/muscular structure to support it. To be immobilized by his fat at that size, he would probably have needed to eat SO much that he gained weight too quickly for his body to adapt, for a long period of time, and intentionally compensated for it with antigravs rather than making any effort to carry his own bulk.
It is also implied that the excessive weight gain is a symptom of a hereditary disease common to the Harkonnen. Rabban is stated to be approaching the Baron's girth, while Feyd-Rautha keeps it in check through his... rigorous physical training program. Neither of these is any less of a monster, though.
The prequels explained that the Baron was originally an exceptionally fit man, in fact fairly obsessive and vain about it. But then one day he was blackmailed into siring a child (Jessica) with a Bene Gesserit and decided to have a little fun with it at her expense. She in turn took the opportunity to tweak his body chemistry a bit.
Same with Bruno Jenkins from The Witches, an entitled little jerk who enjoys frying ants with his magnifying glass and bragging about his wealthy father. The titular antagonists lure him with food and transform him into a mouse. Even in this state, Bruno continues his gluttonous ways and is no help to the narrator.
Early in the Star Wars Expanded Universe, Warlord Zsinj was an enemy of the New Republic and one of the very few humans in Star Wars described as overweight at all. His portrayal in The Courtship of Princess Leia showed him as venal, highly evil, self-important, and very, very stupid. His successes seem to be all related to the size of his fleet and the programs his scientists set up. The X-Wing SeriesRet Cons this, making Zsinj still fat and faintly ridiculous, still highly evil, but also very, very smart, and deliberately cultivating a slightly absurd image that he knows smart people can see past, but he likes playing to an audience.
Hutts, which are specifically said to be lithe and muscular when young and become progressively more obese as they grow older and gather more power, are almost universally disgusting. Almost. There's some record that a Hutt was once a very fair and very popular Chancellor of the Republic.
There is also a subversion in at least one Hutt Jedi, who is implied to get more powerful in the force as he gets fatter, presumably because he has more life force, or something.
The Hutts in general are one of the few races that are immune to the "mind tricks" of the Jedi or Sith, indicating perhaps a naturally strong connection to the force as a species trait.
There's also the Toydarians, who are related to Hutts, are almost as bastardly, and they all have big guts. Though, as extra materials point out, their guts aren't filled with fat, but helium. Which explains why such a being can fly around on those puny wings. Fatness may be the least of their unfortunate stereotyping.
Another fat bastard human featured in Tatooine Ghost - one of Leia's fellow survivors of Alderaan is fat enough to need a hoverchair. He's small-time compared to the other bad guys in the fic, but a greedy wretch nonetheless.
This trope is closely examined in Robin Hobb's The Soldier Son trilogy. After Nevare grows extremely fat as a side effect of a disease, he notices how people's attitudes towards him have changed drastically to the worse. People who haven't even talked to him make fun of his size in his presence, and some are even openly hostile. He has to prove to those he meets that he isn't a bastard, because they tend to assume he is.
Inverted by Harold Lauder in The Stand, at least in the novel. Harold is a sympathetic character while a fat nerd—it's only after he loses weight, becomes moderately attractive, and gains a few levels of competence outside of bookish pursuits that he does a Face-Heel Turn.
The Bibledescribes the assassination of a very fat king who leaks excrement when he is stabbed. He oppressed the Israelites for eighteen years, which perhaps explains why this particular detail was included by those who wrote the account.
The Ancestress, an early villain in Bridge of Birds. Li Kao recalls her as a beautiful, scheming concubine who butchered all of her rivals and their children, then had the Emperor murdered and set herself up as a regent over her weak-willed son for years, where her extravagance ran the empire into the ground; her son got blamed and subsequently executed in a coup, while she retired to a life of luxury. By the time we see her, however, she has gained two hundred pounds out of overindulgence. When she finally meets her end, in a gruesome manner typical to this series, she is described as blundering around the room crushing her own guards with her monstrous weight while Henpecked Ho pursues her with an axe.
Tim Powers uses this villain archetype in several of his novels — Leo Friend in On Stranger Tides and Loretta deLarava in Expiration Date are both described as extremely, grotesquely fat.
In Robert E. Howard's Conan the Barbarian story "The Phoenix on the Sword", Ascalante sneers at one of the nobles who thought they had hired him as "the fat baron of Attalus."
A few of the antagonists from the Sherlock Holmes short stories such as Jephro Rucastle from The Copper Beeches,Charles Augustis Milverton from the story witht the same name, and Blessington (or Sutton) from The Resident Patient.
A Song of Ice and Fire is filled with this trope. There's Yezzan zo Qaggaz, an extremely wealthy slave owner who is called (behind his back) the Yellow Whale for his yellow eyes and the fact that he is so obese that he cannot stand unassisted. Ser Amory Lorch isn't as fat as him, but still quite fat. Magister Illyrio is morbidly obese and seems to be decidedly amoral.
However, this trope is subverted with Lord Wyman Manderly, who is another morbidly obese person who at first seems to be this trope, but it turns out this was a ploy and he is actually a pretty good guy.
This trope is also somewhat subverted by the above-mentioned Yezzan zo Qaggaz. Although one of the foremost slavers in an extremely brutal slaver society, he also happens to be one of the lesser evils among the slavers, arguing that Yunkai should not break a peace treaty while others hope for the riches that will come with sacking Meereen and apparently taking better care of his slaves than most. Well, aside from occasionally sending them out to be fed to lions or having his slave girls raped by giants for his amusement. Yeah.
Kalchan, Skif's cousin in Take a Thief, is described as having rolls of fat bulging over his waistband. He's physically abusive to Skif (and sexually abusive to the underage server Maisie.)
In the original Sleepover Club books, one of the girls' enemies was an overweight school bully named Amanda Porter, known to them as "Fatty Bum-Bum." They explained that although they usually disapproved of calling people cruel names, they make an exception for Amanda because she was so cruel to everyone else.
Vassily Zhukovsky, head of the Russian Mob in Los Angeles, in Mr Blank is nicknamed "The Whale." He is not a svelte man.
Laman Griffin in Angela's Ashes. He is Angela's overweight cousin who forces her to sleep with him, makes Frank empty his piss pot and sloppily eats chips while refusing to share them with any of Angela's kids — they have to lick the newspaper he throws out because they are so hungry.