Raidashir was younger brother to the Persian King Ardashir I of the Sassanid Dynasty. Raidashir was a bloodthirsty warrior and in the later years of Ardashir's rule, he was feared even by his elder brother. Prominently known as the reviver of the Zhayedan, Raidashir helped expanded his brother's kingdom and quelled the Roman threats.
He was exiled by the King for practising a faith other than Zoroastrianism, the more popular religion in Persia at the time. References about Raidashir appear throughout the Sassanid Dynasty's history, spanning from 3rd century AD till its fall in 642, and could refer to different persons with the same name. However, recent studies reveal that another Raidashir had created a cult of black magic practitioners whom the leader of was given the title Rai Shah.
The cult grew rapidly in India after the fall of the Persian Empire to Caliph Umar in 642 AD at the Battle of Nahavand. The title, Rai Shah, was changed to Raja Rai according to the local dialect in India at that time. The name of the cult was unknown but it was believed to be the forerunner of the ancient Indian custom of sacrificing the wife of a dead husband to the Death Goddess Kali. By the time the Muslim Moghul Empire had spread its power in the late 13th century and devoured the Chola Kingdoms, all the traces of the ancient cult in India had disappeared.
Raidashir himself was rumoured to be exiled by the kingdom and his existence was last recorded in Langkasuka in the 12th century Peninsular Malaysia.