Ahriman (Syriac: ܡܠܟ ܚܫܘܟܐ melech kheshokha: king of darkness) is the name of an entity also called “evil.”
Ahriman is a conscious entity, not simply a concept, but a sentient and malevolent force opposed to the will of God. Another name or term that Manichaeans often use to reference the evil one is the King of Darkness.
Manichaeism teaches that the reason we grow old, get sick and die is because the physical shells we inhabit were designs of Ahriman and not because of God.
The King of Darkness is a being that rebelled against the Father of Greatness and in so doing, captured a portion of the Divine Light, resulting in the formation of the illusion of matter and the creation of evil.
Other names and/or titles of Ahriman include: Tiamat, Maya, Satan, Lucifer, Mara, Shaytan, Iblis, etc.
The worship of Ahriman is forbidden in Manichaeism.