XII. The Twelfth Imam, Muhammad, known as al-Mahdi (b. 256/868)
The twelfth Imam lived in hiding under the protection and tutelage of his father until the latter's death. Then he went into "occultation". In other words, he became hidden from the eyes of ordinary men and appeared only to his Deputies (see p. 92.)
In the year 329/939 his "greater occultation" began. It will continue as long as God wills, but when he does appear once again, he will erase evil and injustice from the world.