wikishia:Featured Article/2016/15

Al-Nuwwāb al-Arbaʿa (Arabic: النواب الأربعة) [literally meaning The Four Deputies] were the deputies to Imam al-Mahdi (a) and the connection between him and the Shi'a during Imam's Minor Occultation. They are also called al-Nuwwāb al-Khāṣṣīn (the Special Deputies). They were among the trustworthy old companions of previous Imams (a) who were in contact with Imam al-Mahdi's (a) Wukalā (agents) in most remote places of the Islamic land appointed one after another by Imam (a) and delivered Shi'a's messages and requests to Imam (a) and his answers to them.

Disappearance of Imam al-Mahdi (a) happened in two periods: the Minor Occultation and the Major Occultation. The former took 70 years and prepared the ground for the latter.