Fallen angel names include Lucifer, Beelzebub, Leviathan, Asmodeus, Berith, Astaroth, Verrine, Gressil, Sonneillon and Belial. The Book of Revelation and Christian tradition hold that Lucifer led one-third of the angels in a rebellion against God's plan for humankind. Lucifer and his forces were defeated and cast down from heaven. The fallen angels became demons, and in modern usage the two terms are generally synonymous.
Christian demonologists hold that fallen angels have the same characteristics as their heavenly counterparts; they are immortal spiritual beings with preternatural intellects. The New Testament contains several accounts of Jesus Christ exorcising demons from possessed individuals, such as the man with the unclean spirit in Mark 1, or the Gerasene demoniac in Luke 11. Exorcists classify demonic activity into different levels. All believers are subject to ordinary temptation, where the demon tempts someone to sin. Demonic infestation occurs when an evil presence affects houses or other inanimate objects. Diabolical oppression takes the form of physical ailments, ranging from mild discomfort to severe illness. Diabolic obsession is manifested by obsessive thoughts from which the sufferers cannot free themselves, often tempting them to suicide. The most dangerous form is full possession where the demon takes total control of a person's body.