He begins by writing about how Satan has taken command of Hell and acts to leave Hell and make his plan of messing with Earth come to fruition. He also talks about how Satan demonstrates antagonistic qualities because he is wants to cause pain to things and get in the way of the protagonist. This article helps to strengthen that Satan is portrayed as an antagonist because he wants to foil the protagonist’s plan.
Steadham, John M. "The Idea of Satan as the Hero of "Paradise Lost"" Proceedings of the Philosophical Society 120.4 (1975): 253-94. JSTOR [JSTOR]. Web. 6 July 2015. Mr. John M. Steadham writes in his article about Satan in “Paradise Lost” that Satan is a hero because he displays heroic qualities, such as going where no one wants to go, being the center of the poem, and embarking on a journey to stop the antagonist from fulfilling his plan. He argues that the general public cannot look at Satan objectively enough to discern him from hero or villain. The viewing of Satan as a hero rather than a villain does not support the thesis but the article does show that audiences do not look at Satan