Source: Heaven Unleashed, pg(s). 38
Izzdeveron the Assailant was a balor and nascent demon lord who led an assault on a hold in the Prime Vallation. He was repelled and slain by the star archon Olquinhat and her forces, but unleashed an unholy explosion upon his death that separated the bastion from Heaven and sent it adrift toward the Maelstrom. That bastion is now known as the Entropic Hold.