We tried to kill him with 20-25 people on the day of a new server opening so had little horde intervention.  The problem is he spawns about 20 lvl 55 non-elite guards each time you tag him that stun, and he has about 1 million health, a cleave for >2000 on normal hits, a huge knockback, and resets if you pull him too far out of his hut or if he goes to charge someone back on the path behind his building (a safe forming area free of guards).

It would probably take an organized group of 40 people or more to bring him down now.