Yazidism has a unique twist: the Earth is ruled over by a being known as Taws Melek or the Peacock Angel. When God creates the angels, He instructs them to bow before no other being but God. When God creates Adam, He instructs the angels to bow before him. Only the Peacock Angel refuses, and when asked why, he argues that to bow before Adam would be to disobey God's previous order. For his wisdom, God rewarded the Peacock Angel with dominion over Earth and humans, and tasks him to guide them. The Peacock Angel, if you haven't already guessed, is typically identified with Satan/Lucifer/Iblis, but here he is recast as the first among the angels as opposed to an evil adversary.
Also, it's worth mentioning that "Satan", in the original conception, was more title than name. The Jews envisaged the Satans as participating in judging souls: it was their duty to declaim a soul's sins and test their faith, more so for the sake of the mortal than for Yaweh, of course.
Lastly, SMTIV: Apocalypse takes things in an interesting direction... Lucifer is, unwittingly, still a servant of YHVH: he is the scourge YHVH uses to drive humans to him and to punish the sinful. Lucifer could never actually threaten YHVH: only humans are capable of downing him; this is why Krishna and the Divine Powers needed Flynn. When both Lucifer/Walter and Merkabeh/Jonathan are defeated in YHVH's realm, they regain their consciousnesses and fuse to form Satan in order to battle YHVH.
Man I really need to go through and play the SMT series...
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Kill anyone who gets in the way... Actually nevermind that... JUST KILL EVERYONE! - Kyojiro Kagenuma - WoTS 2 PSN:kingmalak