Interestingly enough, satan per se doesn't really figure much in the Old Testament. Some Christian theologians see him as the serpent in the Garden of Eden, yet curiously enough, most renditions of said snake were likely depictions of Lilith, who was sometimes depicted as a half-woman/half-snake Lamia, and snakes were a frequent rendition of Middle Eastern Earth (Chthonic) goddesses. Outside of Genesis, the Devil was almost non-existent and was usually considered the Lord of the Djinn in the most recent of the older books. Exodus has Baelzebub (Lord of Lies, though this was later conflated with the Lord of the Flies (a pun in English and Hebrew)).
In the New Testament the word Satan was used frequently, but the term likely derived from the early Hebrew for advocate or lawyer. In this respect, Satan was the voice of secular reason, in opposition to the message of messianic faith. While it's difficult to determine what the figure of Christ actually said (the earliest accounts were written some 200 years after he died), Satan was evil because he undermined faith, not because he actually performed antisocial acts. It was only later, as Christianity became more polarized (and more state-sanctioned) that Satan became the embodiment of all evil. Note also that the Fall of Lucifer from the heavens post-dated Christianity by several hundred years, and was primarily an invention of Rabbinical clerics involved with the Kaballah. It's also worth noting that the Phoenician Ashtoreth, the Navigator Goddess, was known as the Morning Star (Lucifer is Latin for Bearer of Light), which strengthens the argument made several times by different scholars that Christianity was almost certainly not an extension of Judaism, but was instead Phoenician in origin.
So, yes, the Devil has definitely received a bum rap over the years.
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