Imperius was present at the Pandemonium Fortress when Iskatu, a demon in service to Diablo, led an assault on the fortress. Iskatu wore the Pandemonium Loop, a ring given to him by Diablo that sowed fear amongst the angels defending the fortress. Imperius was unaffected by the loop however, and hacked off Iskatu's arm. Iskatu fled the field of battle, and the ring was lost.