Satan (a.k.a. The Devil) is the personification of evil. Modern Christian mythology casts Satan as an angel who defied the will of God. He was cast out of heaven with his followers and was condemned to rule over hell. He is seen as “the father of lies”, the tempter of Adam and Eve, the tormentor of mankind on earth, and the torturer of mankind in hell.
But this has not always been Satan’s lot. Before modern Christianity condemned him to hell, Satan had a very different mythology associated with him.
Definitions of Satan
"Among those books of the Hebrew Scriptures written before 300 BCE, the term 'satan' (root word 's'tn') appears often. The word is derived from the original Hebrew verb 'satan' which means 'to oppose.' The Septuagint translation of the Hebrew Scriptures into Greek was widely used in the early Christian church. They translated 'satan' as 'diaboloc' from which we derive our English term 'devil' and 'diabolic.'"
- — Religious Tolerance web site
Satan as an adversary
There are several different definitions when the term 'satan' is used in early writtings. One is a person acting as an accuser or enemy. In 1 Samuel 29:4 , the Philistines were distrustful of David, fearing that he would be a satan. (translated "adversary" or "someone who will turn against us"). In 2 Samuel 19:22 Shime-i apologizes to King David. The King rejects the apology, saying that they should not be a satan to each other (translated "adversary" or "opponent"). In 1 Kings 5:4 , King Solomon is talking to Hiram, the King of Tyre. He says that now that there is neither satan nor bad luck to stop him, he can build the Temple. (translated as "adversary", "enemy", or "one who opposes"). And in 1 Kings 11:14 , God raised up Hadad the Edomite as a satan against Solomon. (translated as "adversary," or "opponent").
Satan as a divine messenger
Another use of the Hebrew term translates as a divine messenger sent by God as an adversary. In the story of Balaam in Numbers 22 , God appears in a dream, and tells Balaam to go with the princes of Moab to meet Balak. But when Balaam sets out the next morning on his donkey, God is angry with him for his attempt to evade God's wishes, and he sends an angel/messenger to kill Balaam. The donkey sees the angel and takes evasive actions, but the angel is invisible to Balaam, who beats the animal. The donkey asks Balaam why he had beat her three times and Balaam (who doesn't seem to realize that a talking donkey is particularly odd) replies that the donkey has mocked him. The angel then appears and explains that he has come as a satan to kill him. (translated as "one who opposes, "withstand," "adversary")
Satan as a divine councilor
Another use of the Hebrew term translates as a member of God's council, sort of a chief prosecutor. In 1 Chronicles 21:1 , Satan, "a supernatural evil emissary," acting on God's behalf, influences David to hold a census. The census is taken, but God becomes angry for reasons not given in the writings. God then offers David his choice of one of three punishments: a three year famine, three months of fleeing before his enemies' armies, or a plague throughout Israel. David selects the plague and God kills 70 thousand men. There is no mention of the number of women or children, or even if the 70 thousand includes women and children. In 2 Samuel 24 , the identical event is described. However, this time, the text states that God influences David to hold the census, yet still becomes angry that it was done and punishes the Israelites with a plague. Some scholars consider the writings in 2 Samuel to be the original account. It is believed that when Samuel was finally edited (circa 560 BCE), the editors thought that all supernatural actions (good and bad) came from God. When Chronicles was written over a century later (circa 400 BCE), the author viewed God as operating indirectly through his helpers.
In Job 1-2 , Satan is clearly described as one of the members of the court of heaven. Here, Satan is portrayed as a servant of God whose task it is to dutifully carry out evil deeds at God's instruction. And in Zechariah 3:1-7 , Satan is again portrayed as a member of God's council, where he objects to the selection of Joshua as the high priest.
The transformation of Satan
The Protestant Christian Bible closes the Hebrew Scriptures with the book of Malachi, written circa 397 BCE. The Catholic Bible continues with seven other books called the Apocrypha. They both pick up the story again at the birth of Jesus. This gap of several centuries is commonly called the "intertestamental period." By the end of the "intertestamental period" Satan had taken his place as the ruler of hell and the enemy of God and all mankind.
So what happened between 300 BCE and 33 CE to alter the previous theological ideas?
During the last three centuries before Christ's birth, the portrayal of Satan in Judaism changes. From the middle of the 5th century BCE until 53 BC and even later, the Jews picked up a number of concepts from the official religion of Babylon called Zoroastorism: specifically, the concept of angels, of Satan (Angra Manyu aka Ahriman, the God of Evil) and of the immortality of the soul. Of the three main divisions of Judaism (Essenes, Pharisees, Sadducees) in the 1st century BCE, the Essenes seems to have focused the most on Satan. The Zoroastrian/Persian dualism concept appears in Jewish writing: God, formerly the source of good and evil, becomes wholly good; and Satan as profoundly evil. History is suddenly viewed as a battle between them. No longer was Satan simply God's prosecuting attorney, helper, or lackey. Satan, and his demons, suddenly become humanity's greatest enemies.
In the Apocryphal texts, the Book of Tobias mentions the demon Asmodeus and the angel Raphael, betraying the Persian influence. In the Book of Enoch, the word “Satan” occurs in both singular and plural forms and, in Ecclesiasticus, he is identified with the subtle serpent of Genesis. Finally, the Book of Secrets of Enoch describes his rebellion against God and consequent expulsion from heaven. Note that none of these texts are part of the officially recognized Hebrew Scriptures. They are very late additions to Hebrew theology, with dates of writing ranging from 200 BCE to about 100 CE. Ironically, one of the reasons that the Protestants use for their rejection of these texts within the bible is that neither Jesus nor his followers quotes directly from them, yet the entire context of an all-evil opponent of God who falls from service and resides over Hell is taken from these late period stories.
Clearly, Jesus and his followers were familiar with these texts in the early part of the first century C.E. Mythology had completed Satan's transformation from the loyal servant of God to his most significant adversary.