"Do you really wish to know?" — Spoilers from the books and/or adaptations to follow!
Ozzrel is a very large, named alghoul. Kill him and take his head to the Royal huntsman to receive 200 
in addition to some experience points.
Ozzrel is found in the crypt in the outskirts, but only on a second visit having completed Buried Memories for Mikul.
Associated quest
Notes
- Talking to the Royal huntsman is not a necessary in order to unlock the secondary area of the crypt and gaining access to Ozzrel (i.e. you need only complete Buried Memories).
- Ozzrel can be a difficult foe, but he does turn his back which is a good time to strike.
- Using potions and oil can also help defeat him more quickly.
- If you have difficulties beating him, then Igni hit-and-run tactic can be useful. Especially if it is boosted by Place of Power and Circle.
- There is no need to kill him while he is in the room where he is found. He can be led to a more well-lit area, which can be better than holding a torch if a torch is being used to see in the dark.
- His head is not the only prize in his room. After he is defeated, make sure to get the Red Meteorite ore.