AHRIMAN was born dark and stinking — and seems to have gotten steadily worse. He spawned the demonic world-threatening monster AZHI-DAHAKA and sprinkles wickedness wherever he can.
Like SATAN, his main goal is to fill the world with as much evil as he can so it will destroy itself. Current reports indicate that his policy so far has been highly effective.
The good news is that Supreme God AHURA-MAZDA is his total opposite and has taken steps to ensure nice things happen — after the inevitable Apocalypse, that is. So plump for him, unless you happen to prefer the Satanic Death Evil Doom Heavy Metal Cult.