Ratu is the protector or guardian of the Zoroastrian faith, the chosen one of Ahur Mazda . In the Zoroastrian hierarchy, the rhatu stands above the mobedan moped .
Ratu proves its status through passing the test of fire ( Ordalia ). Ratu separates lies from truth in matters of dogma and is considered infallible. According to the Zoroastrians, the last rut on earth was the highest Zoroastrian priest Adarbad, son of Mehraspand ( pehl. Adurbad i maraspandan ) during the reign of Shapur II (309-379 AD). Adarbad went through several vessels and trials, during one of which molten copper was poured onto his chest. Adarbad, the son of Mehraspand completed the restoration and codification of the Avesta and made a trial of heretics and false teachers.