Folah, Satan is not the ruler of anything. He is the "adversary". The Hebrew word "Satan" simply means "district attorney", nothing more. His job is to "prosecute" by tempting people away from Hashem. Read the book of Job. It's all spelled out there. God himself creates both good and evil, and delights in them both, according to Isaiah. This means that there are created beings called angels to administer both. There is a beautiful kabbalistic parable:

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A wealthy king wanted to turn his kingdom over to his son, and wanted to do it while both were still alive. He had reason not to trust his son, so he devised a test. He told his son he had to remain chaste until his wedding, or he wouldn't inherit the kingsom. Then, the king went to a prostitute, who was also a very loyal subject. He offered her a million gold coins if she would seduce him son. She agreed to try. The king is of course Hashem, the son is man and the loyal prostitute is Satan. Satan obeys God and does his job 100%, as commanded, no matter how distasteful. Did the son fall for the temptation? A true Jewish parable has no ending
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