Satan, the Adversary
Satan is the Devil, the prosecuting angel. The word Satan simply means an 'adversary' and is used in the Bible of any opponent or enemy, the root meaning of the word being 'to oppose', with no supernatural overtones. In the opening chapters of the Book of Job, however, 'the Satan' (with the definite article, so the meaning is 'the Adversary' and Satan here is not a proper name) is an angel who appears in the council of the angels in order to challenge God to put Job to the test.
Similarly, in the book of Zechariah (3:1-2) the angel whom God rebukes for his evil designs upon Jerusalem is 'the Satan'. In the book of I Chronicles (21:1) 'Satan' (without the definite article) is used as a proper name. Interestingly, in the parallel story in the book of Samuel (2 Samuel 24:1) it is God, not Satan, who entices David to count the people. The later book of Chronicles, reluctant to ascribe the temptation to God, substitutes Satan. In subsequent Jewish literature Satan is personification of both a demonic power outside man and the urge to do evil in the human psyche. Very revealing of the demythologizing tendency in rabbinic thought is the saying (Bava Batra 16a) that Satan, the yetzer hara (evil inclination) and the Angel of Death are one and the same. Maimonides (Guide of the Perplexed, 3:22) praises highly this saying as indicative of what he considers to be the only possible way of understanding the figure of Satan. Maimonides is hardly correct in this, so far as the rabbis are concerned, since many other passages in Rabbinic literature do conceive of Satan as a supernatural figure who hates the Jews and brings their faults before the heavenly throne.
This is certainly how Satan is depicted in Jewish folklore in which numerous superstitious practices are based on belief in Satan and his demonic hosts bent on doing harm. On the whole, it can be said that the figure of Satan does not occupy any prominent role in Jewish theology, though it would be incorrect to say that Satan is entirely ignored. In modern Jewish theology, even among the Orthodox, Satan, as a baneful force outside man, is relegated to the background if he is considered at all.