The name "Satan" appears only sporadically in the Old Testament, and when it does appear, his adversarial role often appears to be as more against humans than against God. The Satan plays a major role in the book of Job as an accuser of humanity before God; it is God who allows the Satan to wreak havoc upon Job. Elsewhere in the Old Testament he is rarely mentioned. One curious reference occurs in the book of I Chronicles, which reports that the Satan moved King David to take a census; a parallel passage in II Samuel reports that it was God who was responsible.
Satan figures much more prominently in the New Testament and in Christian theology. In some Christian theologies (as reflected in Milton's Paradise Lost), Satan is believed to have been an archangel named Lucifer who turned against God before the creation of man. According to this view, he waged war against God, his creator, and was banished from Heaven because of this. The creation story found in the book of Genesis reports that a snake tempted Adam and Eve to partake of the fruit of the Tree of Knowledge of Good and Evil. In the Jewish tradition, the snake was always taken to be literally a snake; the story tells us the origin of how the snake lost its legs. (Interestingly, scientists have discovered that primitive snakes did indeed have legs.) Later Christian theologies interpreted this serpent to be Satan, to the point where many American Christians are unaware that the actual Hebrew text does not identify the snake as Satan. In Eastern Orthodox Christianity, Satan is one of humanity's three enemies, along with sin and death.
According to most Christian eschatology, Satan will wage a final war against Jesus, before being cast into Hell for all eternity. One novel view is that Satan will be restored in the last days and become a good angel again.
In various Gnostic sects, Satan was praised as the giver of knowledge, sometimes with references to his name of Lucifer or "the light-bringer". Some claimed that the being imagined as God by Christians and Jews was in fact Satan, as a world as imperfect as ours could not be created by a perfect God.
Satan is worshipped by Satanists. Some satanists claim Satan is a real being; others view him as a symbol for the animal desires of humans; still others view him as a symbol for the rebellious or independent aspects of humanity.