As alpha predators and clever pack hunters, wolves have often been feared and hated by humans. They frequently preyed on human livestock and, in Europe, humans themselves to the extent that serious efforts were made to wipe them out of the region. This reputation bled over into fiction where wolves were portrayed as nasty, savage and rapacious predators seemingly bent on devouring everyone they could. Give them some intelligence and they'll be cruel, nasty and sadistic.
Because wolves are pack hunters, this makes them even more dangerous. One wolf is easily capable of killing an unarmed human, but bring out a dozen or so and suddenly they can devour anything in their path, especially the ill or weak humans we want to protect most like women, children and the elderly.
Note that while this trope usually comes in the form of a pack of wolves, it can equally apply to a lone one. Bonus points if it's much more dangerous and persistent than a single wolf has any right to be.
Compare and contrast the more recent trope Noble Wolf, which features wolves as noble, proud, reasonable or even outright heroic. When the two tropes intersect, they will still be very dangerous and not to be underestimated or disrespected.
See also The Big Bad Wolf and Hellhound. Compare animals that share similar reputations, such as bears and sharks.
One episode of Pokémon portrays a pack of Houndour like this. However, it becomes Subverted when it's revealed why.
The Wolf in Chirin No Suzu. Ruthless and vicious, he kills whatever he can sink his fangs into — including Chirin's mother. Subverted because Chirin soon grew fond of the Wolf, seeing him as a father. In fact, near the end, after killing Wolf, he soon felt sad and realized that revenge wasn't satisfying.
In an early storyline, the normally friendly wolf youkai Royakan is unwillingly transformed into a monstrous, berserk beast that can vomit up packs of equally vicious normal-sized wolves.
A later storyline introduces a whole tribe of wolf youkai, infamous for eating humans and destroying entire human villages in the process. Led by the humanoid wolf youkai Kouga, these wolves destroy three human villages (including Rin's, killing everyone there including Rin herself) before encountering Inuyasha's group. By the end of this first encounter, however, Kouga becomes enamored enough of Kagome that he forbids his tribe from attacking humans and they become Noble Wolves instead.
A Dracula Lives story featuring Solomon Kane has Dracula saving the man from a pack of wolves before inviting him to his castle.
Idées Noires: One gag has a man lost in the snow wandering around thinking he is doomed. Then he sees lights in the distance and thinks it's a city, but it turns out to be the Glowing Eyes of Doom of a group of wolves.
The wolf shown in the beginning of the film/comic 300 is depicted as demonic and threatening.
Fenris from the Lucifer comics manages to take revenge for his fellow mythologies by stomping into a story arc almost entirely populated by Judeo-Christian characters. When one challenges him for this he points out that before humanity cowered before demons they feared the wolves beneath the trees, proceeding to pretty much become the Big Bad through raw Badassery.
The Secret of Kells, when Aisling sics her wolves on Brendan as he's traveling through the forest in search of oak galls. Later inverted when Aisling sics them on the Vikings that are about to kill Brendan and Aidan in a Big Damn Heroes moment.
Frozen features a scene in which the heroes are pursued by a pack of wolves similar to the Beauty and the Beast example.
The Grey has wolves as the film's primary antagonists, especially the Alpha. The wolves are shown as cunning and brutal, often attacking from stealth or when the humans are otherwise compromised. The film does mention several times that the only reason the wolves are so vicious is because the crash victims have wandered too close to their den.
The name of the eponymous protagonist of Lone Wolf McQuade is clearly supposed to invoke this.
In the third Riddick movie, a wounded Riddick wakes up after being left for dead on a barren planet by the Necromongers. He is quickly sighted by a pack of alien wolf/dog creatures who pursue him. Subverted later on when he discovers a lone pup, whom he eventually raises to become a loyal companion.
As the cast of Day of the Animals sleeps peacefully after their first day of backpacking, a lone wolf suddenly attacks Mandy and scars her face badly. This forces her and her husband Frank to split up from the others to get to the local forest ranger point.
Inverted at first in The Fifth Elephant then played straight after the wolf who's keeping them in line dies and they revert to their natural instincts, which include killing any werewolves they come across, (even Angua). She doesn't begrudge their hostility though, she knows and accepts that they have some pretty good reasons to hate werewolves.
J. R. R. Tolkien liked this one. Packs of intelligent wolves (called Wargs) threaten the main characters of both The Hobbit and The Lord of the Rings. However, Tolkien does make a distinction between regular, rarely dangerous wolves, and the decidedly more monstrous Wargs, who always directly serve the bad guys in his legendarium.
In a story by Saki, two men, the heads of feuding houses, are badly injured and trapped in the woods. No sooner do they decide to put their differences aside do they hear a rustling in the bushes. One man can see their presumed rescuers coming. When the second man asks if they are his men or the other man's men, the first man answers with one word. "Wolves."
The Dresden Files: While he's watching the Alphas in action Harry notes that, in this age of guns and helicopters, humans have forgotten why we used to be afraid of wolves, and that there are several very good reasons.
The Wolves of Willoughby Chase: Im an alternate England where packs of wolves roam the 19th century Yorkshire countryside, the young heroine is almost killed when one such pack attacks a train. She's only saved when the man sharing her carriage stabs the wolf that's got in with them to death.
In A Song of Ice and Fire, most wolves are considered Savage Wolves, but the direwolves adopted by the Stark children vary according to the personality of their owner and how well they're trained. Among the most savage are:
Shaggy Dog, belonging to Rickon, who is untrained and as feral as his owner. He is known to attack unprovoked, and bites Maester Lewin.
Nymeria, belonging to Arya. She was originally well-trained, but since being driven off early in the first book, she has gone feral and now leads a huge pack (numbering in the hundreds) of ordinary wolves which threaten both livestock and man throughout the Riverlands.
The boys go hunting for food, and run into a wolf. You'd think it would easy for four of them to take down one single wolf, but it's not. They are helpless until the dog, Maxie Jr., shows up to distract the wolf, at witch point they gain the upper hand and kill it.
Later on, when they need wolf pelt to survive the snow, they go looking specifically for more wolves, and find a whole family in a cave. Although three of them plan to take on the entire cave (which would have been suicide), some Divine Intervention from Sol comes in the form of a lightning bolt that kills most of the wolves, leaving only three for the humans to fight.
The antagonist, Loki, also takes the form of a crimson-colored wolf. He is not seen with any other wolves, but attacks Mickello directly once every year in an attempt to kill him or injure him.
In Dan Abnett's Gaunt's Ghosts novel His Last Command, Gaunt remembers how Colm Corbec would tell stories of wolves circling "the stranded, the unlucky, the lost" to bring them down; his current situation, being stalked by an unseen Chaos creature, reminds him.
As when a prowling Wolfe, Whom hunger drives to seek new haunt for prey, Watching where Shepherds pen thir Flocks at eeve In hurdl'd Cotes amid the field secure, Leaps o're the fence with ease into the Fould:
Fenris, the giant wolf fated to devour Odin himself.
Fenris' sons, Hati and Skoll, who are destined to devour the moon and sun.
The negative perception of wolves is directly responsible for the modern Swedish name for wolves: varg, meaning "killer" or "strangler". Folklore had it that saying wolves' proper name (ulv) would call them, or at least cause bad things to happen, which lead to wolves being called what they were seen as (murderous brutes). Problem was, this became so wide-spread and went on for so long that varg ended up as the proper name for a wolf, and the folklore about speaking their name being bad remained.
"Peter and the Wolf" depicts the titular wolf as a the primary antagonist, with him eating at one of the other characters and attempting to eat the rest.
While Dungeons & Dragons depicts wolves themselves are depicted as morally neutral and they are even available as companions for heroic characters, the monstrous Worgs (taken from Tolkien's "Wargs") and Winter Wolves are invariably evil and dangerous.
Madfang Ragewolf from Patapon 3 is one of the main antagonists of the game. He is linked to an archfiend and represents the Deadly Sin of Rage.
Spiral Knights has Wolvers, they are quick, depending on the breed can inflict status effects, and if they're accompanied by an Alpha, their attack increases, players will often be killed by a pack of wolvers at least once in their in-game life.
In Red Dead Redemption, wolves are tough, highly aggressive, persistent, have a knack for showing up precisely when you don't need them do, love to kill your horses, and attack in waves. You gun down four or five of them, look around, and the coast seems clear, only for another batch to arrive just as you put your gun away.
In World of Warcraft, many Wolf-type enemies have an ability that causes them to howl and alert other nearby wolves of the player's presence, effectively swamping you if you're not very careful.
In Dragon Age: Origins you'll occasionally run into packs of wolves as enemies. There's even one specific encounter on the overworld map that can be especially vicious on higher difficulties, a rare form of That One Random Encounter.
In Skyrim, it's not uncommon for a player to find themselves attacked by two or three wolves at once. They're easy to kill, but they can become Paranoia Fuel if you can hear the howls but are unable to see them or know the direction the howls come from. The worst part of the wolves is that they may infect you with Rockjoint plague which severely reduces your fighting ability.
Cataclysm: Wolf packs are one of the worse non-zombie threats roguelike. They're made all the worse by the fact that their letter color can make them very hard to spot before they're on top of you.
In Minecraft, wolves normally mind their own business, and can even be tamed and used as guard animals but if you attack a wolf, it and its whole pack go berserk and try to kill you.
MediEvil: Latter portion of the cemetery stages feature wolves. In order to leave the cemetery, you have to fight two stone wolves which guard it.
In Age of Empires II, Age of Empires III, and Age of Mythology, wolves are the archetypical wild predator of the wilderness. If Age of Empires II is played without the expansion, wolves are the only predator in a game, that ranges geographically from Europe to the Middle East, to Asia. Age of Mythology is also the only game of the series where wolves can be hunted for food, otherwise they are just a menace deadly to villagers.
Back in I and II, wolves were one of the Barbarians' recruitable creatures (stronger than both goblins and orcs). In both of those games, Barbarians were defined as an Evil town...
Gothic: Wolves, and other creatures in the wolf family, can be dangerous depending on your level, because unlike with most other enemies, it is difficult to lure them to you one at a time, so you'll usually have to deal with entire packs.
Tomb Raider (2013) often features packs of wolves attacking you. Even worse, one level has you enter their den to get supplies.
Neopets - While the pirate Captain Scarblade is a savage pirate, not all Lupes, a wolf-like species, are evil or vicious.
The Wolf Apocalypse in Gunshow, which was caused by God who had forgotten Jesus's birthday, and was trying to make it up to him.
In No Rest for the Wicked, the woods are known to house wolves, which is why Perrault refuses to believe that November came through the woods alone. However, the actual wolves appear only as skins in Red's cottage.
Metalocalypse - the band's therapist tries to attack them but falls out a window. He survives the multi-story fall, but then gets his arms ripped off by wolves who live in the compound (though he survives that and gets a new pair of mechanical arms).