Ahriman (Syriac: ܡܠܟ ܚܫܘܟܐ melech kheshokha: king of darkness) is the name of an entity also called “evil.”

Manichaeism

According to the Manichaean Faith, Ahriman is a conscious entity, not simply a concept…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.”

The Manichaean Faith also 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. A being that rebelled against Abba d’Rabbuta and the Living Spirit 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.
Manichaean Glossary

Other names and/or titles of Ahriman include: Tiamat, Maya, Satan, Lucifer, Mara, Shaytan, Iblis, etc.

The worship of Ahriman is forbidden in Manichaeism.

Monijiao Buddhism

Ahriman is equated with Mara of Buddhism. According to Monijiao Buddhism, the evil one (Mara) is the cause of corruption in the world among religious and political leaders, and has caused people of the world to lose faith and trust.¹ Worshiping or giving any type of honor to Mara is forbidden in Monijiao.

In Buddhism, Mara is referred to as a tempter and evil one.

He is often called “Mara the Evil One’… or Namuci (lit. ‘the non-liberator’, i.e., the opponent of liberation). He appears in the texts both as a real person (i.e. as a deity) and as personification of evil and passions, of the totality of worldly existence and of death. Later Pali literature often speaks of a ‘fivefold Mara’…1. Mara as a deity, 2. the Mara of defilements, 3. the Mara of the Aggregates, 4. the Mara of Karma-formations, and 5. Mara as Death.
Buddhist Dictionary, Nyantiloka

References

¹ The Deep Ocean of the World, by Tenzin Bhikkhu of the Monijiao Buddhist Monastery.