Despite having a reputation for cuteness, seals are also well-known for being predators, which aren't exactly well-liked. Some, like the leopard seal, eat penguins, which is a bit of a problem, considering that people love penguins. And so, when they're not Ridiculously Cute Critters, fictional seals are often portrayed as either mindless brutes or malevolent monsters.
This trope mostly applies to large, stereotypically aggressive seal species such as leopard seals and elephant seals. Small ones, such as the harbor seal and the harp seal, are much more likely to be portrayed as Sweet Seals. If a small seal does act evil or aggressive in fiction, it's a case of Killer Rabbit. There's some aspects of What Measure Is a Non-Cute? involved here too; generally, the larger seals that prey on penguins and other seals are portrayed more negatively in fiction than the smaller ones that mostly eat fish.
This trope also includes sea lions. They're different from seals — for instance, they have ear flaps, and flippers that allow them to "walk" on land — but are also included due to being highly similar to them in most if not all other respects; in fact, the entirety of the immediate clade that includes them both consists of marine mammals of the same general body plan and carnivorous behavior, including walruses and fur seals (the latter being the sea lions' closest relatives). And their closest relatives? Bears.
Compare Wily Walrus (since walruses are related to seals), Threatening Shark and Devious Dolphins. Contrast Sweet Seal. Subtrope of Sea Monster. Not to be confused with Sealed Evil in a Can. Also not to be confused with Navy SEALs, although their targets may very well be scared. Has nothing to do with the singer Seal.
- In Happy Feet a leopard seal is a recurring antagonist of the penguin heroes. Elephant seals also recur in both films; they make no attempt to harm the heroes, but they are terrifying. The second film goes into the "beachmaster" social order noted under real life. Also in the second film, a leopard seal and an elephant seal cross paths, and the leopard seal, a species generally considered The Dreaded in penguin stories, flees in terror.
- Ice Age 4: Continental Drift: One of the pirates is an elephant seal named Flynn. He's more of a Cloudcuckoolander than a truly threatening villain, though.
- In The Pebble and the Penguin, there is a seal who tries to eat the main protagonist.
- In Penguins of Madagascar, the penguins are shown to despise leopard seals, which are portrayed as mindless penguin killers with Black Eyes of Crazy. Curiously, the leopard seals seem to be the only animals in the movie who are not humanized in any way, which is especially strange considering that one of the heroes is a harp seal.
- In Romeo & Juliet: Sealed with a Kiss, Prince, a Composite Character of three antagonistic characters (Tybalt, Prince Escalus and Paris) from the original play, is a gigantic elephant seal who terrorizes the other seals on the beach, and even threatens to eat Romeo at one point.
- In Eight Below, when Max is investigating a dead orca as potential food, a leopard seal lunges out of the carcass and chases him off. Max manages to lure it away by running off with a piece of meat, with the seal chasing him beneath the ice and leaving the other dogs free to eat until it figures out whats going on and doubles back, lunging at the dogs from behind and crippling Maya.
- The Tizheruk is a cryptid/sea monster from the mythology of the Inuit of northwestern Alaska and the islands of the Bering Sea, supposedly resembling a very large, long-necked seal. It's said to be highly aggressive and anthropophagous, snatching people off of piers to eat them. It is hypothesized by some cryptozoologists to be a very northerly relative of the leopard seal (despite the tropics and the entire Pacific Ocean separating them).
- The Jungle Book: Subverted in The White Seal by Kotick, an albino seal who lives in the Aleutian Islands and makes it his quest in life to find a home where the seals won't be victims of the fur trade. He comes to tell the other seals he found such a place... and when they refuse to listen to him, beats the shit out of every one until they agree to follow him.
- Percy Jackson and the Olympians:
- The Telekhines are literal monsters that are often compared to seals — specifically sea lions — in appearance.
- The spirit of the East River, a hostile and unfriendly minor god, looks like a humanoid combination of a seal and a wolf.
- The Winter Of The World: Amicac the Sea Devourer is a seal the size of a war galley, and he's ferocious enough to make a leopard seal seem as meek and mild as a lamb. His appearance in the third book (The Hammer of the Sun) is... impressive.
- Dungeons & Dragons 3rd Edition had the Sea Lion, a seal/lion/shark hybrid creature that was noted for being a highly aggressive coastal predator.
- Bunyips are enormous seal-like monsters with shark-like teeth (and sometimes dorsal fins), and are infamous for their ferocious and aggressive natures, insatiable appetites and willingness to attack and devour anything smaller than themselves. They often compete for food and territory with other predatory pinnipeds, such as leopard seals.
- The ice sheet over the Antarkos Ocean is home to ferocious, ten-feet-long leopard seals that literally tear penguins out of their skins before devouring them — their territories can be identified by the bloody, discarded penguin skins left lying around.
- The setting's take on selkies, in their natural form, look like vaguely humanoid leopard seals, complete with a vicious array of teeth. And while some are friendly enough when they're not snowing you, some would as soon eat a player character as look at one.
- Battleborn: Thaddeus from the DLC story operation Toby's Friendship Raid is a fat rich anthropomorphic leopard seal alien in a suit. With the use of his stolen factory ship convoy, he plans to build a mech army that will help him take over Solus. While he talks and acts like a pompous entitled upper-class nerd, he nonetheless looks menacing and is just as dangerous. He does however become much evil looking in the 10th playthrough of the operation wherein he decides to use the alias he uses as a blackmarket kingpin, The Lorrian.
- The Battle Cats features the Sir Seal line of enemies, which are all rather tough to defeat. Two of them, the first Sir Seal and Sir Metal Seal, are motivated purely by craving for attention.
- Donkey Kong Country: Tropical Freeze: Pompy the Presumptuous is a circus sea lion who serves as an entertainer for the villainous Snowmads. He's surprisingly scary for the first boss: not only is he enormous — one of the biggest members of the Snowmads — but he's one of the only three bosses in the game to get heavy metal music — the other two are the penultimate and Final Boss!
- Dragon Project: Crossing over with Wily Walrus and Our Dragons Are Different, Volatile Valenga and Fanged Mercura are a pair of seal dragons with power over fire and ice respectively. Wherever they go, they drastically change the climate and temperature of the surrounding area within a short time period, causing massive destruction towards the environment and any other life near them, and ruining Pamela's swimming classes while teaching the Hunters. Both of their Tablets allow you to craft the Fire Soul Bow and the Water Soul Spear respectively.
- Kingdom of Loathing portrays seals as demonic entities spawned in the Infernal Abyss, and Seal Clubbers, unlike in Real Life, are Barbarian Heroes that protect ordinary people from their wrath.
- The New Zealand Story: The main villain of the game is Wally, a leopard seal who kidnapped all but one of the kiwis from Auckland's Zoo with plans to sell them to various zoos throughout the country.
- Futurama: Not quite a monster, but in the episode satirizing Mutual of Omaha's Wild Kingdom, the Beachmaster (Bender's elephant seal counterpart) is an obnoxious Jerkass whose only response to being told he's just crushed a bunch of helpless seal pups is to gloat about how he now gets to sire more of them.
- The Penguins of Madagascar: Subverted with Hunter, a friendly leopard seal pup who Private saves from a fishing net. Her family are all right too, when they aren't trying to eat the heroes.
- Pingu: The seal/sea lion/walrus... thing was so unnerving that the episode it appears in, Pingu Dreams, is banned in a number of countries.
- The Simpsons: In one episode, Homer reads an article in Reader's Digest magazine which describes the bark of a sea lion as a sound all polar explorers dread.
- Wild Kratts:
- Martin and Coach the sea otter have a close call with a Steller's sea lion, a major predator of sea otters.
- The first penguin-themed episode also features the penguins' major natural predator, the leopard seal.
- The Wild Thornberrys: Played with in the episode, "Tamper-Proof Seal", where the Commvee becomes blocked by a group of northern fur seals and their aggressive beachmaster, because the Commvee happened to be parked on the seals' breeding ground. Eliza has to negotiate with the beachmaster by offering his group plenty of fish to eat.
- Pelagiarctos, an extinct relative of the walrus, was a macropredator, specialised to hunting prey as large as other pinnipeds.
- The Southern Elephant (Beachmaster) Seal fits the trope: a massive creature with a Darwinian social ethos, one where the largest and most dominant males ("Beachmasters") ruthlessly enforce their dominance over the majority of lesser males and gather the females together as exclusive harems, fighting and defeating other males who try to challenge. (The majority of males remain un-mated and single). It's kind of evocative of some nightclubs at two in the morning. Fittingly, beachmasters can grow up to 4 tons, meaning they're Large and in Charge!
- Although there is at least one instance of a leopard seal killing a human, they actually tend to subvert this trope when meeting humans. There have been a few stories of divers coming face-to-face with a leopard seal, only for it to react with curiosity, or even playfulness. One such encounter resulted in the seal offering dead penguins to the diver thinking that he was starving and needed food.
- Bizarrely, it has been observed that male fur seals rape penguins. Scientists speculate that they are sexually frustrated young males that were unsuccessful in obtaining females of their own species as partners.