The twelfth Imam of the Ahlulbayt Imams. His name is the same as the Prophet's name and he has many titles for instance, Al Mahdi, Al Qaem (Upriser) and Baqiatullah. you and I am Allah’s proof upon them”. Imam Al Mahdi (as) 

He has had two occultations:

Minor Occultation:

It started at the year 260 A.H. and continued until the year 329 A.H. It lasted seventy years, when the people were connected to him by his 4 special representatives: Uthman Ben Saied Al Omari, his son Mohammad Ben Uthman, Hussein Ben Rooh and Mohammad Ben Ali Al Sumari.

Major Occultation:

It started at the year 329 A.H., after the death of his last special representative. It will last for unknown period of time until the day when Allah choses for him to fulfil the world with justice and peace as it has been filled with oppression and injustice. He does not have a special representative during this period but he has general representatives. They are the just scholars. It has been narrated from Imam Al Mahdi (as) that “Follow the narrators of our Hadiths in The occurring matters, as they are my proof on you and I am Allah’s proof upon them”. It has been also narrated from Hassan Al Askari (as) about their rights that: “Whoever from the jurists that was protecting himself from sins, keeping his religion, against his desires, following the order of his master (ALLAH), it is obligatory upon ordinary people to follow him.”The sayings about Imam Mahdi (as) that he is the son of Imam Hassan Al Askari are numerous. Even some of the Sunni reference books have mentioned this. Sheikh Najmuldeen Al Askari in his book (Al Mahdi, the promised, the awaited) and Sheikh Lutfullah Al Safi Al Gulpaigani in his book (Muntakhabul Athar Fi Al Imam Al Muntadhar) have mentioned some of the sunni references.We have been ordered to wait for him as it has been narrated from The Prophet of Allah (s) that: “The best of worship is awaiting the (Faraj) relief.”“Whoever from the jurists that was protecting himself from sins, keeping his religion, against his desires, following the order of his master (ALLAH), it is obligatory upon ordinary people to follow him.” Imam Al Askari (as)

Some of the non-shia references that have mentioned the birth of Imam Al Mahdi (AS) in the 15th of Sha'ban of 255 AH and that he is the son of Imam Al Hassan Al Askari (AS).

• Mohammad Bin Talha Al Halabi Al Shafei in his book (Matalebul Seol Fi Manaqebe Aal Al Rasool) has mentioned that: "the twelfth chapter about Abul Qasim, Mohammad bin Al Hassan … Al Mahdi, Al Hujah, Al Khalaful Salih, Al Muntadhar … He was born in Seru Man Ra'a." He also said: "Al Mahdi is the son of Abu Mohammad Al Hassan Al Askari, he was born in Samura."
• Serajul Deen Al Refaei in (Sehahul Akhbar) has said: " Imam Hassan Al Askari has left the Man of the Cellar, Al Hujah Al Muntadhar, Waliu Allah, Al Imam Al Mahdi."
• Ibn Khalkan in his book (Wafayatul A'ayan) has said: "His birth was on Friday the mid of Sha'aban in the year 255 AH. When his father passed away he was 5 years old. His mother's name is Khamat. Also it has been said Narjess."
• Mohammad Ameen Al Baghdadi Al Sewedi in (Sabaeik Al Thahab) has said: "Mohammad Al Mahdi, who was 5 years old at the time of the death of his father."

References The book (Al Mahdi Al Maw'ood Al Muntadhar) (The Guided, the Promised, the Awaited) by Late Sheikh Najmul Deen Al Askari. The book (Muntakhabul Athar Fi Al Imam Al Thani Ashar) by Sheikh Lutful Allah Al Safi Al Golpaigani.