Sethir the Ancient is a level 12 satyr located on a branch of the new world tree Teldrassil, north of the Oracle Glade. Sethir is one of the few satyr who is considered to be humanoid, this is most likely to enable the picking of his pockets for the completion of a quest
The objective of the quest  is to steal Sethir's Journal from him without notice.
Attacking Sethir will cause at least 6 Minion of Sethir (level 10 satyr) to appear, making it difficult to retreat back onto Teldrassil without taking heavy damage. It is therefore not advisable to attack Sethir unless you have good backup, or fast feet. Stealthing and pickpocketing is the most advisable route, as it is almost impossible to kill him with his minions. Sethir the Ancient can also teleport so be quick about pickpocketing. However, when he stops at the end of the smaller branch, he can be sapped, pick pocketed, and then killed with none of his minions spawning.