Fenrir Greyback

"I could do you for afters, Dumbledore..."

- Greyback to Professor Dumbledore atop the tower, implying that he's already eaten someone shortly before

Fenrir Greyback is an antagonist in the Harry Potter series. He is a werewolf who follows the Death Eaters, and wishes to amass a werewolf army large enough to defeat the wizards. He was played by the late Dave Legeno in the movies.

Backstory
Greyback was in the First Wizarding War and was a ruthless werewolf who took no remorse in killing. He was either infected as a youth or during his childhood. Unlike other werewolves, he showed a delight in transforming, going as far as to express lupine tendencies and aggression in his human form. He was recruited by Lord Voldemort to act as his enforcer. Greyback joined, not because he believed Voldemort's cause, but because this allowed him access to more victims.

During the First Wizarding War, he was convicted of killing Muggle children, and bought before the Ministry for a trail. However, Greyback was such a good actor he passed himself off as a homeless Muggle man who claimed to be astonished at being in front of a congregation of wizards and disgusted by child killings. Given Greyback's stale smell and scruffy appearance, the court almost believed his homeless story, until Lyall Lupin, Remus Lupin's father, who was a court martial at the time, noticed the signs of Lycanthrophy in Greyback's face. He noted the pallour that set in during full Moon (coincidentally, it was going to be a full Moon the next day) and Lyall said how Werewolves were brutal monsters who should all be executed. Lyall was heard by Greyback, who was enraged, and by the other ministers, who said Lyall should be rounding up centaurs instead. However, Lyall demonstrated Greyback's lycanthrophy to the whole court, and Greyback yelled he would make Lyall pay as he was thrown back outside.

A few days later, Greyback found the Lupin home, broke into young Remus' room, and bit him as he slept. He thus paid Lyall back and gave Lyall a Werewolf with which to live with. Lyall tried to find a cure for Remus but none worked. He eventually learned to put up with the affliction and stress of the infection his son had.

During the Second Wizarding War
He appears in the sixth and the seventh Harry Potter book and their respective movie adaptations. During Draco Malfoy's sixth year, he appeared at Hogwarts thanks to the Vanishing Cabinet in the Room of Requirement. He was with the other Death-Eaters on the Astronomy Tower when Dumbledore was murdered by Severus Snape. He also also set the Burrow on fire with Bellatrix Lestrange.

In Harry Potter and the Deathly Hallows: Part 1, he helped the Snatchers, led by Scabior, to catch Harry, Ron and Hermione and brings them to the Malfoy Manor, home of Lucius Malfoy.

He is later chased away out of the Manor by Bellatrix after the Malfoy Family decides to hand the trio to Voldemort themselves.

In Part 2, he participated in the Battle of Hogwarts. He killed Lavender Brown and began eating her, until Hermione blasted him out a window.