Raxle Berne is an Imperial Enforcer, and vampire. He resides in the Dwemer Ruins of Galom Daeus, and is an Ancient of the Clan Berne. If the Nerevarine is turned by another Berne vampire, he will provide some quests, as he considers them to be a mistake - albeit still of some use.
After retrieving the Quarra Blood potion, Raxle Berne will send the Nerevarine to kill Merta, a vampire who was once a part of the Berne clan but turned rogue and left the clan. Once Merta is dead, he will give them one last task; that they kill 12 vampires belonging to Clan Quarra and Clan Aundae.
Tharer Rotheloth will task the Nerevarine with slaying Raxle Berne in the name of the Tribunal.