Once Eldreth was a wizard who became a free-willed flameskull.
In 1379 DR, the slaver Lanador hired Eldreth and his men to kidnap ten elves from Waterdeep's streets. Unfortunately, unknown to them, one of them was a member of the Agents of the Eye. So the Xanathar supported an adventuring party to enter Lanador's lair. In the central room of the lair were Eldreth and Lanador and in the fighting both were defeated.