Fiore was one of the Adelphi angels, the administrators and bureaucrats of Heaven. After God left Heaven, the Adelphi were in charge of keeping watch on Genesis, the bastard child of an angel and a demon. Unfortunately, the being escaped, killing a Seraphim in the process, and found a host on Earth - the preacher Jesse Custer.
Fiore and his partner DeBlanc tried to make good on the situation by waking Saint of Killers. Unfortunately, the plan backfired. Custer used his newfound Voice of Command to learn all about God's abandonment and to stop the Saint in his tracks. Custer pledged to hunt God down and make Him answer for His failures.
Fiore and DeBlanc were exiled to Earth, where they actually did quite well. They opened a casino in Las Vegas, where they indulged in all the pleasures of the earthly world.