Erjolf is a young Fremennik involved in the quest The Tale of the Muspah. In the quest, he uses the player to acquire a trophy to allow him to pass the Trials, subsequently running away at the first sign of danger, but denying it afterward.
He can be found near the fairy ring (DKS) northeast of Rellekka, in front of the entrance to a cave. This is the start point to the quest.
During The Tale of the Muspah
After discovering the name of creature, he is in the inner cave at the water's edge.
After running away, he is just outside the entrance to the inner cave.
After talking to him after running away, he is at the west coast of the Rellekka Hunter area (by the transport icon in the northwest area).
After The Tale of the Muspah
He can be found on the west side of the southern part of the Snowy Hunter area, next to a canoe (made by the player during the quest) that can be taken to the Jhallan's resting place.