What is Imam Mahdi’s name and cognomen?
Imam Mahdi's name and cognomen are the same as those of the Prophet of Islam. Imam al-Ṣādiq quotes from his grate ancestors who narrate from the Prophet who have said, “Al-Mahdi is from my progeny, his name and his cognomen is like my name and my cognomen, and he is the most similar man to me in regard with his character and behavior.”[1]
[1] Al-Erbelī in Kashf al-Ghommah, vol. 2, p. 521; Sheikh al-Sadūq in Kamāl al-Din wa Tamām al-Ni’mah, vol. 1, p. 286, hadith 1.