Mazdakism (Persian: مزدکیه, romanized: mazdakīye) was an Iranian religion, which was an offshoot of Zoroastrianism.
The religion was founded in the early Sasanian Empire by Zaradust-e Khuragen, a Zoroastrian mobad who was a contemporary of Mani (d. 274). However, it is named after its most prominent advocate, Mazdak, who was a powerful and controversial figure during the reign of Emperor Kavad I (r. 498–531), until he was killed by Emperor Khusrau I (r. 531–579).
Kavad I (Middle Persian: 𐭪𐭥𐭠𐭲 Kawād; 473 – 13 September 531) was the Sasanian King of Kings of Iran from 488 to 531, including a two or three-year interruption. A son of Peroz I (r. 459–484), he was crowned by the nobles to replace his deposed and unpopular uncle Balash (r. 484–488).
Inheriting a declining empire where the authority and status of the Sasanian kings had largely weakened, Kavad tried to reorganize his empire by introducing many reforms whose implementation was completed by his son and successor, Khosrow I. They were made possible by Kavad's use of the Mazdakite preacher Mazdak, leading to a social revolution that weakened the authority of the nobility and the clergy. Because of this, and the execution of the powerful king-maker Sukhra, Kavad was deposed and imprisoned in the Castle of Oblivion. He was replaced by his brother Jamasp. However, with the aid of his sister and an officer named Siyawush, Kavad and some of his followers fled east to the territory of the Hephthalite king, who provided him with an army. This enabled Kavad to restore himself to the throne in 498/9.