Estrion was the supposed lord of Castle Darkstone. He became an ardent follower of Sheru, the Lord of terror, and harnessed that reverence by opening a portal through the Veil so that Sheru himself could manifest in Elanthia, but when he arrives he used a great deal of power calling spirits in an attempt to overthrow or control Sheru's power for himself. When Sheru withdrew after being weakened, Estrion attacked Wehnimer's Landing in 5093 or so to create enough death and spirits to offset all he had drained from the area. He was killed by the residents of Wehnimer's Landing.
This is why Darkstone castle has strange mana storms.
His spirit has made several appearances and his companion Siarl escaped, but has never been heard from since. Estrion was mostly recently the binding spirit that Akhash used to build the wards around Wehnimer's Landing during Beyond the Arkati. Estrion's spirit stated he'd have a price to pay later for the assistance. He has yet to collect.