Wolf

A Wolf was a four-legged carnivorous wild dog which lived in Middle-earth.

Species
There were many types of wolves in Middle-earth, and usually they lived in a pack in the wild. Some of the known wolves are Wargs, White Wolves, and Werewolves. Sauron, during his service to Morgoth, took the shape of a wolf at least once.

In the films
The Fellowship of the Ring, in the book, was attacked by a pack of wild wolves the night after they came down from Caradhras. Gandalf, who addressed the first wolf to attack as "Hound of Sauron" said after the fight was over, that the wolves weren't ordinary wolves because there were no bodies left nor any sign of the wolves at all. During the time of the War of the Ring, Saruman kept some wolves in Isengard. Also Gandalf sees Saruman's wolves while he is Saruman's prisoner at Orthanc.

In Peter Jackson's film trilogy, Wargs are present in The Two Towers. They attack the fleeing citizens of Edoras as they make for Helm's Deep, killing several soldiers of Rohan's small army before returning to Isengard. This attack only happens in the movie and is not used in the book.

In other media
In The Lord of the Rings: The Battle for Middle-earth II: The Rise of the Witch-king there are also Dire Wolves in the Angmar faction.