Angra Mainyu (also known as Aŋra Mainiiu), also called by his Middle Persian name "Ahriman", is the powerful god of evil and destruction and darkness in Zoroastrianism and is comparable to The Devil in some Judao-Christian religions, however, unlike most portrayals of Satan, Angra Mainyu is seen as a deity rather than a demon (though the two can overlap). Like Satan who is the enemy of God, Angra Mainyu is the adversary of his twin brother Ahura Mazda, the Zoroastrian god of light and truth. Angra Mainyu is seen as a chaos god as well as a destroyer deity - although he is also seen as "evil", he is not recognized as a god of evil, though he does come close. His name means "destructive spirit" or "frightful spirit".
In the beginning of time, when Ahura Mazda created all the good things in the universe, Angra Mainyu, out of jealous spite, sent demons to spoil all of creation. Ahura Mazda welcomed his brother benevolently and with words of peace, but Angra Mainyu spurned him, and so Ahura Mazda casted the evil destroyer back into the darkness from whence he came. Then Ahura Mazda said, "Neither our thoughts, teachings, plans, beliefs, words, nor souls agree.".
After Gayomart, the first human was created, Angra Mainyu, banished to the outer darkness by prayer, attacked creation and spoiled the paradise with starvation, famine, lust, disease, sickness, suffering, and death, defiled everything he touched with rejoice. He then shouts in victory, "I have fouled the world with filth and darkness, and made it my stronghold. I have dried up the earth, so that the plants and animals will die, and poisoned Gayomart, so he will die.".
This infuriated Ahura Mazda, who imprisoned his brother in the Absolute Darkness, from which he could not escape to continue his spoil upon the world. But the unholy god did not concede and lured the first human couple, Mashya and Mashyana, into evil. This forced Ahura Mazda into making them mortal. Like the Devil corrupting people into sin, Angra Mainyu seduces people into wickedness.
Angra Mainyu rules over the Daeva, which are similar to demons in other religions. He has numerous assistants who help him fulfill his role as Evil Spirit. The main ones are Akoman (Evil Mind), Indra Vayu (Death), Saurva (Disease), Aeshma (Violence and Fury), Az (Lust, Greed, and Jealousy), Mithandruj (Dishonesty and Lies), and Taurvi and Zairicha, also known as Tauru and Zairi (Fever and Thirst).
During Frashokereti, the Iranian end of the world, Ahura Mazda will bring prepare to destroy Angra Mainyu. But after the humans are no longer enticed by sin and self-indulgence, Angra Mainyu will be pursued by Az, Ahriman's female counterpart. He will beg to Ahura Mazda for mercy. Ahura Mazda cast the wicked god from creation through the abyss from where he first came from, never to be seen again.