So basically he was just a normal demon general at the time of a war. At the time he actually had skin and flesh. However during the war he lost his wife from a bunch of angels killing her. Infernal then was killed by the same Angel who killed his wife. However due to the sheer rage and anger Infernal had, they had transformed their whole body into basically a walking inferno. They basically became a weapon of mass destruction where he killed lots of angels. After the war he became depressed and then resorted to narcotics to sooth his bloodlust and his mourning of his wife.