I actually wrote a paper on evil/the devil/etc. when I was in school in a course on the Hebrew Bible (i.e. the Old Testament).
Interesting thing is that throughout most of the Old Testament, it's actually God who is the source of all evil. Occasionally, he makes use of adversaries (satans) -- both human and supernatural -- but the working of evil is always at his behest.
It's argued that it was only when the Hebrews come into contact with the Persians and Zoroastrianism that the idea of a separate evil arises. Since Zoroastrianism is strongly dualistic (having separate good and evil powers) it's thought that maybe it influenced the Hebrew's beliefs. Even then, though, it's still God that's in control -- satans always act on God's behalf.
Scholars still debate whether "Satan" ever really shows up in the Old Testament as a personal name (most agree that it's just as a title or descriptor. And there's only really one or two places in the whole Old Testament that it's even debated, the rest are obviously just descriptors/titles). It's really only in later works (both Biblical and non) that the character known as Satan shows up.
Anyway, doesn't particularly answer the question, but I always thought it was interesting. Blame it on the Zoroastrians?
