He is captain of the Witch's Secret Police (though only one of his lieutenants is ever seen). His name is derived from the words "maw" (meaning mouth), "morgue", and "Grim" (a foreboding wolf-like figure from English folklore). His name was changed to Fenris Ulf (a figure from Norse mythology) by the author  and this change was incorporated into early American editions of the book. More recent American editions have reverted to the original text.
Maugrim features in the 2005 motion picture The Chronicles of Narnia: The Lion, the Witch and the Wardrobe in which he is voiced by American actor Michael Madsen. While some of the other wolves were real, a lot of Maugrim was created with computer-generated imagery, but there was also a two-year-old wolf, called Ricky, who played the part.
The Chronicles of Narnia
Spoiler warning: Plot and/or ending details follow.
Maugrim is first named when the Pevensie children find a notice signed by him in Mr Tumnus's cave, announcing his capture by the Secret Police as punishment for not handing Lucy Pevensie over to the White Witch. The Lion, the Witch and the Wardrobe is a fantasy novel for children by C. S. Lewis.
Maugrim is first seen when he is acting as a gateguard and messenger for the White Witch at her castle. He takes Edmund's message to the White Witch and bids him come to her presence. Later, Maugrim and one of his lieutenants are sent to the Beaver's house in order to "kill whatever they find there" and then proceed to the Stone Table to wait for the Witch. Peter Pevensie eventually kills Maugrim, which earns him the title Sir Peter Wolfsbane. Peter Pevensie is one of the major characters in the childrens fantasy series The Chronicles of Narnia by C. S. Lewis.
Maugrim is one of the few Talking Animals who side with the Witch during the Hundred Year Winter, although based on the words of Nikabrik in Prince Caspian a majority of the wolves sided with the Witch at this time. It is, however, clear from the mention of wolves among the former-statues (brought "to life" by Aslan's breath) who go to the aid of Peter's army that the wolves either were not all followers of the Witch, or that she saw fit to punish her own by petrification.
"Maugrim" is only one letter different from Naugrim, the Sindarin term for J. R. R. Tolkien's Dwarves. Since Tolkien and Lewis were close friends, one may have influenced the other here. Maugrim may also be influenced by the giant wolf, Carcharoth, in Tolkien's The Silmarillion. Sindarin is an artificial language (or conlang) developed by J. R. R. Tolkien. In J. R. R. Tolkiens fictional universe of Middle-earth, Dwarves are beings of short stature who all possess beards and are often friendly with Hobbits, although long suspicious of Elves. ... In J. R. R. Tolkiens fictional universe of Middle-earth, Carcharoth (IPA: ) was the greatest werewolf that had ever lived. ... The Silmarillion is a collection of J. R. R. Tolkiens works, edited and published posthumously by his son Christopher Tolkien, with assistance from Guy Gavriel Kay, who would later become a noted fantasy fiction writer.