Werewolf army

The werewolf army, led by Fenrir Greyback, was a group of werewolves who intended to infect as many people as possible with lycanthropy in the hope that one day the werewolf community would be large enough to take over the wizarding community. They, particularly Greyback, specialised in attacking children. This way, they presumably hoped that being infected young would cause them to integrate into the werewolf society sooner.

Second Wizarding War
During the Second Wizarding War, the werewolves allied themselves with the dark side, though they were not considered Death Eaters. This is probably because Voldemort didn't trust their half-breed status. Greyback, although he was not branded with the Dark Mark, became the most integrated into the Death Eaters out of the werewolf community. He thought that by becoming affiliated with Voldemort it would be easier for him and his fellow werewolves to get access to people to attack. He also believed that under his rule, the werewolf race would have a higher place in society than under the Ministry of Magic.

Remus Lupin's involvement
"Nearly all of them are on Voldemort's side. Dumbledore wanted a spy and here I was...ready made."

- Remus Lupin on Greyback's pack

Because of his membership of the Order of the Phoenix, Remus Lupin was sent under Albus Dumbledore's orders to integrate himself into the underground werewolf community to serve as a spy for the Order.

Known victims

 * Remus Lupin
 * William Weasley
 * Son of Mrs. Montgomery
 * Lavender Brown

Behind The Scenes
Werewolves would have been indistinguishable from other witches and wizards during the Battle Of Hogwarts as it was not a full moon, which we know as Lupin and Greyback did not transform. Before the Covered Bridge is blown out you can clearly hear wolves, which could have only been real wolves and not transformed werewolves.

Appearances

 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Deathly Hallows