You misunderstand the role the accuser has in biblical literature.
He is not the one that tortures people in hell, and never was, from a biblical standpoint (though admittedly he has that role in catholic dogma.)
Instead, he accuses GOD of being unfair, and practicing misrule! He accuses god of favoritism (Specifically to how he tries to 'save' humans, rather than obeying his own laws, and destroying them utterly for their sins), and proposes his alternative "Do whatever you want" methodology.
Satan literally means "enemy", or "Adversary." If heaven was a legal courtroom, he is the prosecuting attorney, christ is the defense lawyer, and God is the judge.
It is more complicated than that though, because the prosecutor is charging the judge with being corrupt, and asserting that he needs to recuse himself and allow a different entity to officiate; namely, HIMSELF. To prove the accuser wrong (via QED), God has allowed an experiment for a limited time period, during which the accuser has full authoritative command over things (satan is allowed to have dominion of the earth)-- this is all part of the mythic trial of mankind presented in the old testament, and elaborated upon in Revelation. The narrative goes on to state that the accuser, KNOWING his position is faulted (and his time limited), but hating God anyway, wants to punish God, by forcing him to destroy his creation by leading that creation into unforgivable sinfulness. (If he is going down, he is taking it all with him.)
This figurative narrative is repeated many times through both old and new testaments. The concept of the devil being a ruler of a perpetual "hell" comes from dogmatic interpretations of single verses of revelation (often taken out of context), christianized pagan beliefs from older European religions, and a few religiously inspired poems. These ideas became part of the centralized catholic dogma.
The actual reality is that from the biblical standpoint, the penalty for siding with satan is being unmade, and ceasing to exist either physically or spiritually, and this state is eternal-- Satan will join in this fate.