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 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.
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."
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 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 the popular game Wizard101, there is a warg mount on which the player can ride.
In the George R. R. MartinA Song of Ice and Fire book series, wargs are a type of "skin-changer", a human who can enter and control the minds of animals. "Warg" is usually used interchangeably with "skin-changer" in the series, but strictly speaking refers to those who use wolves most often.
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.