The Golden Hearth
He seems to be responsible for the demon invasion in Tarnwood, although he claims he was just looking for something and has nothing to do with the demons.
When the party confronted him at his tower he scared them away, but ended up taking part of Percy’s soul before they left.
While talking to Bewrathon, Percy let slip that he has an Orb of Dragonkin.
When they later returned to Zandar’s tower, they found his tower in rubble and obsidian, Zandar included.