Most fan-made stuff about Eberron in Ravenloft points at the d'Cannith who made the magical nuke and the warforged (his name escapes me) being a darklord, likely of a place resembling what was once Cyre. Alternatively the Lord of Blades would have made for a worthwhile candidate for Darklord status, or Queen Dannel of Cyre for refusing the olive-branch out of pride and dooming her people.