Agril-Shanak is a fiend, a tanar'ri (a greater glabrezu to be specific) that TNO must free in order to complete "Free Dona Quisho's Fiend" quest. If negotiated with properly, the fiend will offer the Heartgrinder, a battle-axe and one of he most powerful weapons in the game. Setting him free does not affect alignment. Watch for Agril-Shanak fighting the greater baatezu Tek'elach in Curst in Carceri.