Muḥammad al-Mahdī al-Ḥujjah (disappeared 878) is venerated by the Ithnā ʿAshariyyah, or Twelver sect, the main body of Shīʿite Muslims. It is believed that Muḥammad al-Mahdī al-Ḥujjah has been concealed by God (a doctrine known as ghaybah, or occultation) and that he will reappear in time as the mahdī, a messianic deliverer.