Dispater, &, is one of the demon princes. He is lawful and has no lair. A spellcasting monster may summon him in the Gehennom with the summon nasties spell, or a lawful demon (usually a prince; Asmodeus, Baalzebub, or Geryon) can gate him in. He is generated with a wand of striking.

Dispater has a lot of hit points, great magic resistance, and powerful spell attacks. In addition, he resists fire and poison. He'll follow you to other levels and try to steal the Amulet.

He will not generally use his spellcasting attacks before he uses up his relatively harmless wand of striking. Therefore it is a very good idea to kill him as quickly as possible.