“the rightly-guided one”  in Arabic, designation of the descendant of the Prophet who is expected to return to rule the world.

See in entry ISLAM in IRAN:
vi. THE CONCEPT OF MAHDI IN SUNNI ISLAMvii. THE CONCEPT OF MAHDI IN TWELVER SHIʿISMviii. THE OCCULTATION OF MAHDIix. THE DEPUTIES OF MAHDI.