Warg
Lore
Wargs are a breed of ferocious wolves, larger and stronger than their ordinary cousins. These huge canine beasts are under the service of the Shadow. They possess a cunning intelligence and some can even understand or use the speech of Men. As a result, it has been theorized that Wargs are descended from the fearsome Werewolves of the First Age or that they are possessed by dark spirits commanded by Sauron. All that is certain is the threat they pose to the Free Peoples of Middle-earth.
Wargs share a close relationship with Orcs, who often use them as steeds. Orkish Warg-riders can frequently be found leading the charge in battle. Wargs are found all across Middle-earth.
Background
The term "Warg" (also spelled "Wearg", or "Vargr" in Old Norse) is an Old English word that means "wolf" or "outlaw." J.R.R. Tolkien likely meant these creatures to resemble the gigantic wolves of Norse and Anglo-Saxon mythology.
All known Warg sightings: