It's like asking whether God is real. Even human phenomena has thought us that there is opposing force to every existing force. For example, where there is positive there also negative force, where there is light there also darkness, where is good there bad. Same goes for God and Satan. God is the good force which is light while Satan the bad force which is darkness. Evidentially, every good things happening in the world is propelled by the force of God. Undoubtably, any bad things in the world is orchestrated by satan. His activities is noticeable through the work of men just as it is with that of God. Now to the question whether Satan is real, yes he is real. He is as old as the beginnig of the world. If you're familiar with the biblical scriptures, you will remember how he made the first man and woman to sin. He was the serpent that deceived Eve that subsequently did same to Adam. It was through Satan sin entered the world which was the first of many to come.