In Norse mythology, a vargr (pl. vargar; often anglicised as warg or varg) is a wolf and in particular refers to the wolf Fenrir and his sons Sköll and Hati. Based on this, J. R. R. Tolkien in his fiction used the Old English form warg (other O.E. forms being wearg and wearh) to refer to a particularly large and evil kind of wolf.
In Old Norse, vargr is derived from the reconstructed Proto-Germanic *wargaz, ultimately derived from the reconstructed Proto-Indo-European (PIE) root *werg̑ʰ- "destroy". In Beowulf, Grendel's mother is described (line 1514) as a grund-wyrgen, which may be translated as "cursed creature of the depths", "bottom-dwelling monster" etc.
vargr (compare modern Swedish varg "wolf") has arisen as a noa-word for úlfr, the normal Old Norse term for "gray wolf" which is related to similar words in other Indo-European languages and is derived from the reconstructed Proto-Indo-European noun *wĺ̥kʷos ("wolf") and, probably also, the PIE adjective *wl̥kʷós "dangerous". These words comprise Proto-Tocharian *wä́lkʷë, Proto-Italic *lukʷos, Proto-Balto-Slavic *wilkas, Old Albanian ulk, Greek *lýkos, Proto-Iranian *verk Sanskrit vṛka, Avestan vehrka, Mazandarani varg, Zazaki verg, Old Persian varka- and Persian gorg, among others, all meaning "wolf". Despite their superficial similarity to Old Norse vargr, the various Indo-Iranian forms are not related to it but derive from *wĺ̥kʷos.
- What is that lamp
- which lights up men,
- but flame engulfs it,
- and wargs grasp after it always.
Heidrek knows the answer is the Sun, explaining,
- She lights up every land and shines over all men, and Skoll and Hatti are called wargs. Those are wolves, one going before the sun, the other after the moon.
Wolves also served as mounts for more or less dangerous humanoid creatures. For instance, Gunnr's horse was a kenning for "wolf" on the Rök Runestone, in the Lay of Hyndla, the völva (witch) Hyndla rides a wolf and to Baldr's funeral, the giantess Hyrrokkin arrived on a wolf.
In popular culture
J. R. R. Tolkien's wargs
Taken from the Old English warg, the wargs or wild wolves are a race of lupines in J. R. R. Tolkien's books about Middle-earth. They are usually in league with the goblins or Orcs whom they permitted to ride on their backs into battle. It is probable that they are descended from Draugluin's werewolves, or of the wolf-hounds of the line of Carcharoth of the First Age. They are portrayed as somewhat intelligent, with a language, and are consciously in league with the Orcs.
The concept of wolf-riding Orcs first appears in The Tale of Tinúviel, an early version of the story of Beren and Lúthien written in the 1920s, posthumously published as part of The History of Middle-earth.
In The Lord of the Rings, they are most prominently mentioned in the middle of The Fellowship of the Ring, where a band of wargs, unaccompanied by Orcs, attacks the Fellowship in Eregion. During the War of the Ring in T.A. 3018–19, wolves prowled outside the walls of Bree. They are here distinguished from "ordinary wolves, hunting for food". Wargs and their riders also appear in The Two Towers.
In the Rankin-Bass adaptation of The Hobbit, they are portrayed as larger than average wolves with ominously glowing eyes. Although Tolkien never provided a fully complete description of the wargs, they do seem to have a conventional wolf-appearance in both The Hobbit and The Lord of the Rings, and they are regularly called "wolves."
Peter Jackson's The Lord of the Rings film trilogy depicts wargs as hyena-like, or even like the extinct, heavier-bodied Hyaenodon. Wargs also appear in Peter Jackson's The Hobbit trilogy but are a more wolf-like breed exclusive to Gundabad compared to the wargs used by the Orcs of Isengard.
Subsequent appearances of wargs in popular culture often owe much to Tolkien. Similar to Tolkien's works, they are often depicted as evil, intelligent wolves that speak their own language, and are often allied with goblin tribes:
- In the Dungeons & Dragons roleplaying game, they appear as minor enemies (spelled "worg").
- In the Castlevania game series, they often appear as large wolf-like enemies. Occasionally they appear as riding mounts for skeletons and the demon Andras.
- In Castlevania: Symphony of the Night, there is a variant known as a Fire Warg which can spit fireballs from its mouth.
- In Castlevania: Dawn of Sorrow, Soma Cruz can absorb a defeated Warg's Soul allowing him to summon the head of a Warg to perform a biting attack on his enemies.
- In Castlevania: Lords of Shadow, Wargs are massive wolf-like beasts take can be tamed and used as riding mounts by Lesser Lycanthropes and the game's protagonist, Gabriel Belmont. The game's first boss is a Giant Warg called the Great Warg which are Wargs that have been blessed with new powers such as greater strength and wound regeneration by Cornell, the Dark Lord of the Lycanthropes.
- In the Gameloft game Six Guns, wargs are one of the animals to be killed in one of the "hunter" missions.
- In World of Warcraft, worgs are a common mob (killable creature) found in forested areas which appear as shaggy wolves with large teeth, and there is a werewolf-like playable race known as Worgen. Like the J.R.R. Tolkien version, the Worgs serve as the mounts of the Orcs.
- In David Clement-Davies's books The Sight and Fell, the wolves are known as the Varg, their self-chosen name, and their god is Fenris.
- In the MMORPG Ragnarok Online Renewal, Rangers can summon a warg as a mount.
- In the 2010 comic book Thor and the Warriors Four by Alex Zalben and Girihiru, the Power Pack team encounter a group of wargs in Central Park that they use to ride to Asgard.
- In the popular game Wizard101, there is a warg mount on which the player can ride.
- In Age of Conan: Unchained wargs are commonly found in the Cimmerian region known as Connal's Valley in addition, in the Age of Conan: Rise of the Godslayer expansion pack concept art of the Khitain wolf mount is labelled WARG CONCEPT.
- In 2005 a German group of musicians formed the (Viking) metal band Varg. This name was apparently not chosen by accident seeing as they present themselves as bringers of a wolf-themed cult (see also their 2011 album, Wolfskult). Besides frequent wolf-related lyrics, they also employ red and black face paint, which is probably meant to resemble Germanic warpaint.
- In RimWorld, wargs are animals that can also be tamed.
- Wolf riders and their wolves are units for the Orc faction in Warlords Battlecry.
- Fenris makes an appearance in Thor: Hammer of the Gods.
- In Guild Wars 2, wargs are large canine creatures with glowing red eyes, a bulky chest and relatively small hind legs. 
- In George R. R. Martin's series of epic fantasy novels, A Song of Ice and Fire, and the popular TV adaptation, Game of Thrones, wargs are people that can temporarily inhabit the mind of a wolf or dog. They are a near-synonymous subset of a skinchanger, a person who can inhabit the mind of an animal, or, in rare cases, even another human. Particular talented wargs can become greenseers, who can glimpse into the past, present, and future. An adage says that one man in a thousand is a skinchanger, and one skinchanger in a thousand is a greenseer.
- Osborn, Marijane; Overing, Gillian R. (2001). "Bone-Crones Have No Hearth: Some Women in the Medieval Wilderness". In Adams, Paul C.; Hoelscher, Steven D.; et al. Textures of Place: Exploring Humanist Geographies. University of Minnesota Press. pp. 354 note 38. ISBN 0-8166-3756-3.
- The "Two Towers" Creatures Guide Collins (November 6, 2002) ISBN 0-00-714409-1