Most Christians believe the answer to that question is obvious: “God created Satan.” But that is not really true. God created Lucifer. That may seem like a small distinction at first glance, but once you understand who really made Satan, it will change your perspective of him forever.
You will never again doubt your authority over the devil. You will realise that he is an inferior being, unable to do anything without the cooperation of a human being. And any fear you have of him will disappear as you realise he is nothing but a big zero with the rim knocked off.