Satan

Satan, "the accuser", is the title of various entities, both human and divine, who challenge the faith of humans in the Hebrew Bible. In Christianity and Islam the title became a personal name, and "Satan" changed from an accuser appointed by God to test men's faith to the chief of the rebellious fallen angels. The Book of Revelation twice refers to "the dragon, that ancient serpent, who is called the devil and Satan," (12:9, 20:2). The Book of Revelation also refers to "the deceiver," from which is derived the common epithet "the great deceiver."