Big Eater/Literature

Thin Characters
"Mr. Croup likes words, while Mr. Vandemar is always hungry."
 * In Plautus's plays, table-companions (a peculiar Roman institution, also called "parasites") are played as comically large eaters, making this Older Than Feudalism. Ergasilus in Captivi, given the run of Hegio's kitchen, causes an uproar not unlike those common in The Slayers.
 * The Redemption of Althalus, by David Eddings: Eliar. Although it's because he's a teenager and he grows out of it somewhat later on.
 * Mr. Vandemar, in Neverwhere.

Her big eating was even Deconstructed in In Enemy Hands, when she was captured and she lost a significant amount of weight because she was only fed standard rations. Her warden was particularly frustrated by this since he was trying to break Harrington psychologically but needed her physically fit for propaganda footage.
 * from Heretics of Dune undergoes a transformation that unlocks his Super Speed powers, and as a consequence, has to consume many, many normal human portions to satisfy his hunger. Justified as his metabolism is accelerated to compensate for the increased energy demands. This is commented upon with amazement by the people who observe him eat.
 * The Hungry Tiger in the Oz books is quite possibly the largest and most powerful tiger in the whole of Nonestica, and has an appetite to match. He is only full once -- after devouring a good portion of a royal banquet.
 * Everyone likes to eat in Redwall, but hares have it as a defining trait. To great comedic effect in most of the books. There's also a sequence in Salamandastron where two runaway Mooks try to keep up with the Abbeydwellers' eating, but since they're not used to eating so much, they make themselves horribly ill and have to be given a "fizzick" which makes them bring it back up.
 * Causes something of a problem in another book; a horde of squirrels has agreed to help a hare find his platoon, but, in order, he:
 * Comes dangerously close to overeating on a piece of the squirrels' waybread, one bite of which is dense and calorie-filled enough to last a squirrel all day
 * Promises three entire loaves of the stuff to an owl they're bartering for info with, when they could have haggled him down to one had the hare not been so desperate.
 * Bitches, moans, and in general makes a whiny nuisance of himself over how hungry he is when the squirrels decide that since it was his bright idea to give three loaves to the owl, he can be one of the three poor schmucks who goes hungry until they can make more.
 * And finally, gorges himself on unripe apples, forcing the squirrels to give him a dose of their own brand of "fizzik" before they can move on.
 * The hobbits from The Lord of the Rings are seen as able to put away large quantities of food. In a normal day, they eat at least seven meals (Breakfast, Second Breakfast, Elevenses, Luncheon, Afternoon Tea, Dinner, Supper, plus whatever snacks they can sneak between). As a reference to this, in the Films, elvish Lembas bread, a small bite of which is supposed to feed a normal man, is consumed in the amount of several loaves each by the sidekicks Merry and Pippin, with only mild indigestion to show for it.
 * In the book, though, it is Gimli who inadvertently eats a day's worth of lembas, having mistaken it for the much less appealing cram (human-made waybread with excellent keeping qualities and the flavour and texture of cheap cardboard) and reacting with delight on finding that it's tastier than the best honey-cakes he knows of.
 * From the Wild Cards series of novels, we have Croyd "The Sleeper" Crenson, who can sleep for as little as a night or as much as several weeks/months. Upon waking, he is always a Big Eater, to the point that there's a jingle about it, and people recognize him by his eating habits.
 * Tales of MU has the burrow gnomes with eating habits inspired by the above-mentioned Hobbits, as well as Mariel the sylph who eats as much as four people in order to keep her hyper metabolism up.
 * Benny from The Boxcar Children book series, despite being only six years old.
 * All the bird-kids in the Maximum Ride series have this, because of super-high metabolism to give them energy to fly. Amusingly, in the first young adult novel, they show up at a restaurant and start to order dinner, and the staff think it's some sort of prank.
 * Most of the Brotherhood boys in J.R. Ward's Black Dagger Brotherhood series. Of particular note are Rhage (who is regularly described or insinuated to be the biggest eater, even amongst the brothers) and The latter is an especially fortunate development since the extreme and very detrimental opposite was the case beforehand.
 * Claudia Kishi from The Babysitters Club 1990s-era juvenile book series is a model-thin junk food addict. Many an eating disorder can be traced to this character.
 * Fitz Kreiner from the Doctor Who Eighth Doctor Adventures. He also has Extreme Omnivore tendencies, and questionable table manners. And, as per usual for this trope, he's incredibly skinny, although when he's not busy running for his life and can have three square meals a day, he doesn't take long to get a bit out of shape. Fridge Brilliance: it's probably due to the fact that by the time he's 33, he's spent about two-thirds of his life either under rationing or traveling with the Doctor. Being on a see-food diet (you know, if he sees food, he eats it) is ordinarily a useful survival mechanism which he probably picked up when he was still a small child.
 * Geronimo Stilton's cousin, Trap.
 * The Librarian in the "Hard-Boiled Wonderland" segment of Haruki Murakami's Hard-Boiled Wonderland and the End of the World is one of these, to the point where most of her salary is used to pay for food. It is explained as an effect of her gastric dilation.
 * Honor Harrington's portions often get comments (and envious stares from her less metabolically blessed colleagues), but then she is a genetically engineered Heavyworlder with a Super Strength and requisite metabolism. Though, given how much exercise she subjects herself to, she probably wouldn't be fat even without her genetic tweaks.
 * The Dresden Files: Harry Dresden says that he "eats like a horse", but is still tall and skinny.
 * Because he actually alternates between eating like a horse, and getting so wrapped up in what he's doing that he forgets to eat. So it comes to about even, overall.
 * A rather horrifying version includes the entire Taxxon species from Animorphs, who have a maddening hunger that makes them eat anything they can -- including any injured member of their species or, on at least one occasion, oneself. This hunger is so powerful that when Taxxons are caught up in it (which is a lot) even the Yeerk inside can no longer control it. To its terror. There's a reason that only lower-ranking Yeerks are assigned to Taxxons.
 * Klößchen (Grunter in the English version) of TKKG is one. His German name means "Dumpling".
 * Harry Potter: Ron Weasley, of course. It's a Running Gag to have him cheerfully stuffing 'self out at the feast at the beginning of every year at Hogwarts, sometimes grossing Hermione and Harry out. In Deathly Hallows, it gets even worse.
 * Zedd from The Sword of Truth. Constantly hungry, and very skinny.
 * In The Shattered World, a thief who'd taken professional pride in his slender physique is cursed to be a Big Eater by a sorcerer he'd attempted to cheat. He downs a huge ale and a platterfull of meat before being thrown out of the bar puking, already feeling his perpetual hunger's return.
 * The classic example of this in literature would be Falstaff in Henry IV, who was always drinking, eating, or sleeping. He also was the namesake for the term falstaffian which is now used to describe these people.
 * Fermín from The Shadow of the Wind blames his thin build to his incredible metabolism, which he displays throughout the book.
 * Mulch, in the Artemis Fowl series. Let's not get into what he eats, please.
 * Lieutenant Hélène Froissy, in Fred Vargas's thriller novels. She is seen eating a lot, and hides food wherever she can, including in the police station; the other policemen know this and use her food reserves as emergency supplies.
 * Graystripe from the Warrior Cats series is called this by other characters, though we don't actually see him eating large amounts.
 * Corwin from the Chronicles of Amber, to the extent where his brother Random once snaps him out of an Achilles in His Tent sulk by showing up with a very large tray of food.
 * Luke in Eight Days of Luke,
 * Josh Pinto in the A to Z Mysteries books.
 * Joel Duffle in Damon Runyan's short story A Piece of Pie, a competitive eater who consumes a huge amount of food during the story, but "does not look as if he can eat his way out of a tea shoppe".

Fat Characters
It actually seem that a Wizard's competency and power is directly proportional to how much he eats and how big he is. As seem with the Dean on Reaper Man (who is easily the fattest wizard of the book, but has the power to cast three ludicrously powerful spells at the same time with a delay, to explode/implode a parasitic supermarket) and Rincewind in general.
 * The Orange Duke in Gianni Rodari's The Adventures of Cipollino.
 * Discworld
 * Most senior wizards spend their days eating huge meals. Most (but not all) of them are overweight as a result. Exceptions include the Bursar (who mostly lives on his nerves) and Rincewind. Their Hogswatch dinner has something like twenty courses, and is considered something like an Olympic sport.
 * Although actually an object, one of the defining traits of the Luggage is that it seemingly eats everything and anything that stands in its way. Just don't ask where all that ends up at, as the characters themselves, who occasionally go to the Dungeon Dimensions (a very bad place), are terrified of wondering.
 * Whether the Luggage fits depends on your definition of eat, since it doesn't do it as a regular life-sustaining action, and when it does do it, what, if anything it gains from it is questionable.
 * Keldas of Nac Mac Feegle clans in general, such as Fiona, as seen in the Tiffany Aching books. When she's sharing a meal with Tiffany, she takes only slightly less than what Tiffany has -- and while Tiffany is a fifteen-year-old human girl, Fiona is six inches tall. Justified as she is pregnant pretty much all of the time.
 * Restauranteur All Jolson combines Ankh-Morpork's finest examples of Big Eater and Supreme Chef in one person, which the city considers a match made in mashed potato heaven.
 * Faddey Bulgarin in The Death of the Vazir Mukhtar, and presumably, in real life as well.
 * Mary Gentle's recurring character Baltazar Casaubon seems to always have a snack at hand. And yes, he's fat... but, to paraphrase Gentle herself, it's more accurate to say that he's a huge guy who happens to be fat.
 * Lula from the Stephanie Plum books is a very fat bounty hunter's sidekick, and is seen eating about half the time she's in the scene. Stephanie herself is one in regards to cake, but is only of average weight. Other big eaters in the series are Stephanie's sister Valerie (during pregnancy) and Bob, the Big Friendly Dog Stephanie and on-again-off-again boyfriend Morelli share.
 * Karlsson On the Roof.
 * Caramon Majere during the Dragonlance Legends series, although he eventually gets back into shape.
 * Oblomov himself and also Tarantyev's buddy Ivan Mukhoyarov (brother of Agafya), who likes to spend his money on delicacies instead of more visible luxuries (if only because people could get suspicious - as he says, they can't see what he has in his stomach).
 * Bruce Bogtrotter in Matilda swipes a slice of cake from The Trunchbull's stash. By way of punishment, she makes him eat an entire cake. (He manages, although he's completely zonked in a food coma at the end.)
 * Winnie-the-Pooh. At the beginning of the first book he cleans out Rabbit's pantry. In the second book he eats Tigger's lunch and Roo's. And he's incapable of carrying a pot of honey from A to B without devouring its contents along the way!
 * Nicely-Nicely Johnson and Violette Shumberger in Damon Runyan's short story "A Piece of Pie". She participates in an eating contest and he is her coach, despite being on a strict diet himself.
 * Nathaniel "Ned" Robbins in Jelly Belly starts out as this. His friends at summer diet camp are straight examples, especially Richard. And Richard's parents.