Satan is understood to be the primary "fallen angel" who leads people away from God and who states that he "will not serve."
Just as geological time, evolution, and genetics are not dealt with in the Bible, since the Bible is a theological history, not a science textbook, likewise there are some assumptions about satan that are not literally correct due to lack of precise information.
Satan is a spirit, in the sense he is not a created being like humans or animals but his "home range" is earthly and of course hell. Because of the way scriptures are phrased, where if action does not take place on earth it takes place in "heaven," people believe from reading the Bible that satan once occupied heaven and fell from there. This is incorrect. The Biblical authors, from Moses in the beginning of scriptures to John the Evangelist in the last book of Revelation PERCEIVED the "stage" of satan's origin and actions as "in heaven." But in reality, satan never occupied heaven proper, nor does he engage heaven in battle in or near heaven proper.