DeBlanc was one of the Adelphi, a class of angels in Heaven who were the administrators, the bureaucrats. They were in charge of keeping Genesis confined after God left. Despite all this responsibility, DeBlanc was bitter. Though the Adelphi were in charge, the Seraphi were the ones who seemed to take all the liberties. The soared about on their big wings, looking menacing all the time.
When Genesis escaped, the blame was put on the Adelphi - specifically on DeBlanc and his partner Fiore. They tried to repair the situation by setting loose the Saint of Killers to find Genesis and the man it had possessed - Jesse Custer.
Unfortunately, their plans backfired. Custer had acquired a Voice of Command from Genesis, and used it to find out the terrible truth that God had left Heaven. He stopped the Saint in his tracks and set out to find God and make him answer for his failures.
For this, DeBlanc and Fiore were banished to Earth. They landed on their feet, however, and opened a casino in Las Vegas where they indulged in Earthly pleasures such as sex and cocaine. They had a good life, although from time to time their pleasure would be interrupted by an extremely powerful person - The Saint of Killers, Jesse Custer - looking for answers.