Farkas

Farkas is a lycanthropic Nord resident of Whiterun, as well as a member of The Circle, the group made up of the most formidable and experienced warriors (and, unbeknownst to the rest of Whiterun, werewolves) in the Companions. He serves as the Dragonborn's shield-brother when searching for the fragment of Wuuthrad in Dustman's Cairn. Like the rest of the Companions, he lives in Jorrvaskr, in the Wind District of Whiterun. Farkas may also be encountered in the wilds, seemingly wandering aimlessly and fighting any aggressive enemy he encounters.
After the Companions quest-line is complete, the Dragonborn can go to Farkas for more work. Eventually he will also give the quest Purity to them.