Jalbert

Jalbert - This guy is a necromancer that can be found in his room and is likely protected by 2 Skeletons. Fairly easy to take out and if careful you can sneak up the stairs to his room and let at least one arrow fly into his unguarded back before he turns to fight you.

Once killed there are some useful artifacts (including a statue) to take plus its well worth a read of a few 'manuals' assuming you have entered this ruin almost from the start

One leaving the room, if your security skills are not hot, a few leaps up some stones will get you past a difficult door