Humans conjure up so many things.
Satan is one of them.
With God following close behind.
Hey fellow, I think theres consequence with behaviour and this manifests from what you choose to believe. If you believe there is a devil, you can mislead yourself by ascribing him in others, which to me is creating an enemy.
Well, the funny thing is that a Muslim is not really required to "believe" in Satan. Belief/Iman in the Quranic sense is reserved for God, Angels, The Books, The Prophets, and the Day of Resurrection... that's it. So I don't "believe" in Satan, like I believe in God.
But I do believe satan exists because he is mentioned as an entity in the Quran. As for the exact nature of that entity (whether it is a shadow of us, or an independent being)... well, I dont know.
I think thats the same view of Christinity, a fallen angel?
If there was such a being, they were probably just some part of the intergalactic group which landed here, and got into trouble by opposing the faction that ended up winning.