Lich-Necromancer of considerable power, main force behind the Army of the Dead
Necromancy is not a common pursit for liches but Tersoal was an expert. He was also an expert at concealment and misdirection, and so when the party broke into the Necropolis of Arech and slew his accomplices Torunn Yalastair and Cullinan, they did not manage to find Tersoal.
Neither did the Blades of Wisdom and Mercy when they purged the remainder of the Army of the Dead at the end of 1602, nor the Hollow Knights when Surya sent them after him in 1608.
Tersoal remains at large, an extremely devious and dangerous creature.