This type of thought began with Zoraster and creates a dualistic rather than unified view of the world. I personally think it's spiritual cancer.
Satan is Judeasim was gods bouncer... The word means adversary and he was the tester/challenger of the prophets-see Job, etc. Satan was also NOT the serpent of Eden in Judaesim (but that's another whole story).
Pre-judaesm it seems the word Satan was based on the Egyptian Set.
In terms of Christianity, I think that the whole Satan thing was twisted as a type of bogyman to scare people into obeying the church (misusing gods bouncer? lol).
There is also a gnostic school that considers that Satan and the Serpent are actually the True God and that Jehovah is actually an elemental Demi-urge who got above himself and as a jealous god became a tyrant over man and usurped the place of the True God of Unity etc. See the legend of Prometheus. The idea is that this friend of man wished for humans to remember and become as Gods, etc.
Personally, I have a scientific background and am a devoted skeptic about everything. I see all these myths as saying something about the human psyche and all can be learnt from.
But I don't go for any type of duelsistic thinking. God, if there is such a creature, is ALL, is the sum of all the forces in the Universe (I prefer just to call God the Universe-it's a less loaded term! lol). Thus the Yin/Yang of Taoism is one of the greatest teChing symbols. The universe is a play of opposites man/woman, fire/water, black/White, but all these things are two side of the SAME COIN, th problem is only when folks dont see and keep the balance-then things start to go pear shaped! I wish you good luck with your spiritual journey-enjoy it!



