Abdullah ibn Zamra narrates from Ibn Mati` al-Himyari (Ka'ab al- Akhbar) that he said: "... Hazrat Mahdi (as) who will appear is from the line of Ali. He [Hazrat Mahdi (as)] will make the world an entirely different place. With the Prophet 'Isa (as), son of Maryam, he will bring evidence against the Christians of Rum and China. The Qaim Mahdi (as) is descended from Ali. (He is a sayyid.) HE [HAZRAT MAHDI (AS)] IS THE ONE WHO MOST CLOSELY RESEMBLES THE PROPHET 'ISA (AS) IN GOODNESS, APPEARANCE AND MORALITY. Allah will give the majesty He gives to the prophets to him, too. He will give him virtues and intellect...
(Sheikh Muhammad bin Ibrahim Nomani, al-Ghaybah al-Nomani p. 169)