In The Batman, there was The Cluemaster. After losing a rigged game show as a child, he spent decades plotting revenge against everyone involved, spending most of his time eating the lifetime supply of chocolate he got as a consolation prize from the show. When his revenge plan was actully put into motion, he had become incredibly obese as a result.
Francilee, a No Celebrities Were Harmed version of Paula Deen on Scooby-Doo! Mystery Incorporated, suffered a major blow to her career thanks to a lapse in judgement (ironically similar to Deen herself at the time of the episode's airing). Seeking revenge, she faked her death and masqueraded as the Gluten Demon, a hugely obese monster who began to devour all the unhealthy foods in Crystal Cove. Thanks to cartoon physics, she devours pretty much all of the food in town, but unlike cartoon physics, she remains morbidly obese from all the weight she gained eating as the Demon at the end of the episode.
In the Clue Club episode "The Missing Pig Caper", the main culprit is Mr. Glut, a fat millionaire who wanted to buy the missing prize pig so he can eat him. When Larry interrogates him, he is enjoying a "light snack", a six-foot-long sandwich.
The Lethal Chef Lunch Lady Ghost in Danny Phantom. It's never stated if she is a constant eater, but she's obsessed with food (especially meat) one way or the other.
Eddy from Ed, Edd n Eddy may apply. He is known to have a big desire towards jawbreakers. In a Christmas special, he even devoured Jimmy's gingerbread village within seconds.
Taz from Looney Tunes is a classic example. He will eat any species of animal and can devour large quantities of food (and other things) without ease. When he starts spinning, he always sends crowds running away. (In his own show, he's still a glutton, but not all-too villainous.)
Piggy from Pigs Is Pigs. He may not be evil, but he's the one who causes the most problems for his family in the short. He's a classic greedy pig, always sorrowfully pining for food and whenever he gets the opportunity to eat, he usually tries to eat it all by himself. When he hears dinner is ready, he knocks over his siblings on the way to the table and then when the table is set, devours most of the food set out to feed his family of eight, and doesn't care that his family must now go hungry. When he's captured by a scientist and force-fed for an entire day, he becomes a morbidly obese shadow of his formerly tiny, cute self. When offered more food, he begins slogging down more turkey and explodes before waking up in terror.
Oleander from Sushi Pack. She's usually only a villain because she wants to eat the Sushi Pack, who are admittedly living pieces of sushi. She also has the moniker "The Gulping Gourmet," which explains her large frame. According the coloring books, Oleander is her last name; her first name is Fatima.
Despite being very small, Lucius on Jimmy Two-Shoes has been known to eat a buffet in seconds, keep a well of chocolate all to himself, and put cake on the top of his birthday wishes.
The eponymous Serial Killer from the 1949 Looney Tunes short "Bye-Bye Bluebeard" starring Porky Pig was one, and in fact, this trait was his undoing. As the fiend was about to execute poor Porky using a homemade guillotine, the mouse that Porky had been chasing earlier distracted him with what Bluebeard thought were popovers, but were actually bombs. The villain ate them, and exploded.
Sally Struthers in the Starvin' Marvin episodes. (The second one even had her look like Jabba the Hutt.) She steals much of the food donated to the Ethiopians.
Cartman. In one episode, it is shown that making him thin would actually make him a nicer person.
Rob Reiner. His Knight Templar attitude toward smoking is contrasted with overeating every second of his life
In one episode of The Real Ghostbusters, an accident caused Slimer to start transforming into a Super-Powered Evil Side that the team dubbed "Big Green", who was far more of a glutton than the regular Slimer (and unlike Slimer, incredibly dangerous.)
Rugrats: Angelica, much of her bad behavior involves stealing cookies, which are her favorite food. In an episode where Chuckie's discovers what life would be like if he were never born, Angelica boots Tommy out of his house and is so overindulged by DiDi and Stu she's become a giant.
In Peppermint Rose all the bugs of Bugooyna eat everything, to the point that there are no flowers or trees left in their land and they'll happily dine on visiting humans. Queen Beeteelya plans to eat the peppermint roses, which would plunge the land into ruin.