Maugrim (known by some records as Fenris Ulf) is the secondary antagonist in The Chronicles of Narnia: The Lion, the Witch and the Wardrobe, a ferocious talking wolf and the head captain of the White Witch's Secret Police at the very end of the Long Winter. He was loyal to the White Witch.
Maugrim first led the raid of Tumnus' Cave where the Faun Tumnus was captured and his home left in tatters. Here, Maugrim left a letter to warn and intimidate others passing by, making an example of Tumnus. Maugrim encountered the human boy Edmund Pevensie while guarding the White Witch's Castle courtyard after Edmund mistook him to be a stone wolf.
He escorted Edmund into the Witch's throneroom, and after the Witch learned from Edmund his siblings were at the Beavers' Dam, she ordered Maugrim to find them and arrest them.
Howling to call his wolves, Maugrim led them all to the dam. Once they arrived, he ordered his wolves to "Take them".
The wolves broke inside, finding the dam empty but also a secret tunnel. When they emerged from the tunnel's exit, they found a fox whom Maugrim demanded to tell him where the Human Fugitives had gone, threatening that "[his] reward [was his] life. It's not much, but still."
The Fox told Maugrim the Humans headed north, and so he ordered his wolves to smell them out before they took off, sparing the Fox.
Eventually, Maugrim and his wolves caught up with the other Pevensie Children and the Beavers at a frozen river. One of his wolves restrained Mr. Beaver while Maugrim threatened Peter to put down his sword, mocking him that someone could get hurt, and chuckling when Susan said Peter should listen, smugly stating, "Smart girl."
Maugrim falsely promised that if the Pevensies left Narnia their brother would leave with them, mocking Peter further that it wasn't the Children's war, lying that the White Witch only wanted Peter to take his family and leave Narnia. He threatened he would not wait forever nor would the river. Unfortunately, the river did indeed not wait as it burst (due to spring starting to return to Narnia), washing the Pevensies and Beavers away.
Angered, Maugrim and his wolves tracked down the Fox and delivered him to the Witch, declaring him a traitor, rallying the enemy in the Shuddering Woods. The Witch turned the Fox into stone and commanded the Wolves to gather the faithful, that if it was a war Aslan wanted, it was a war he would get, demonstrating by casually turning a butterfly to stone as well.
Maugrim later spied on Aslan's Camp until being exposed by Susan Pevensie with the sound of her horn. Peter arrived, drawing his sword and met Maugrim in a standoff while she and Lucy fled into a tree. At first, Maugrim mocked Peter, stating they'd been through this before, they both knew Peter did not have it in him to kill. Aslan arrived, subduing Maugrim's follower but did not interfere with Peter's battle. Maugrim growled to Peter, "You may think you're a king, but you're going to die. Like a dog!!!"
The Captain of the Secret Police lunged at Peter, accidentally impaling himself on Peter's sword, killing him.
His fate in the book is similar, although there are a few differences: Namely, Maugrim taunts Peter after the latter draws his sword inches away from Maugrim's face. Maugrim then pounces him only to be impaled on the sword, letting out a yelp as he dies. It is not specified whether his killing himself was deliberate or if Maugrim let his arrogance blind him.