Sebastian Lort is a Breton mage who resides in Rimerock Burrow and possesses the Rueful Axe, which was given to him by Clavicus Vile after his daughter, who worshipped Hircine, contracted lycanthropy and he begged Clavicus for a cure as he could not bear to see his daughter in such a bestial form. He is the primary antagonist of the quest "A Daedra's Best Friend."
Barbas, when asked, will tell the Dragonborn how Sebastian's daughter worshipped Hircine, the lord of the hunt. At some point he found out she became a werewolf and he wished to cure her of this. Sebastian asked Clavicus Vile to help cure her and Clavicus gave him the axe.
The Dragonborn will be asked to bring back the axe to the statue of Clavicus Vile.