Haha !
There is little evidence (outside of the Jewish documents incorporated into the bible) that belief in a spiritual opponent to YHWH existed before the second temple era (that is, after the Babylonian exile of the Jewish elite).
Most scholarship sees the rise of belief in two figures who are opposed to each other and spoken of in terms like good and evil, and light and darkness as the influence of Zoroastrianism on the Jewish elite.
The garden of Eden story in Genesis is pure mythology, best described as a foundation myth.
Crazyguy's explanation is also importatn in understanding how Jewish thought developed.