Details of Imam Mahdi:

The following are facts taken from the Ahadith of Rasulullah( Sallallahu alayhi wasallam):
Name and Title:
His name will be the same as that of (Rasulullah Sallallahu alayhi wasallam), i.e. Muhammad. In addition, his father's name will be Abdullah. His title is Al-Mahdi, meaning the guided one. The Holy Prophet Sallallahu alayhi wasallam also called him Khaleefatullah, meaning "the Deputy of Allah".
Family lineage:
Imam Mahdi will belong to the tribe of Quraish and the family of Hazrat Fatima (radiyallahu anha), the offspring of Hazrat Imam Hasan (radiyallahu anhu).
Character:
He will have the character and morals of Rasulullah (Sallallahu alayhi wasallam). In one night Allah will grant him unique qualities of faith, piety, leadership and knowledge. Hence the titleMahdi.
Birthplace:
He will be born in Madinah Shareef.
Physical features:
He will have a broad forehead (with not much hair on the front of his head) and the bridge of his nose will be raised.
Signs before his appearance as the Mahdi:
The world will be filled with a great amount of injustice and oppression. There will be widespread evil in which all people will be heavily involved.
Muslim countries and their people will have become so weak that even animals would defeat them in battle.
Muslims would be totally disunited, hence their state of weakness. On the other hand, the Kuffaar (Jews and Christians) of the whole world would be united under one leader. Their rule would spread over the entire world, and would reach as far as Khaibar, a mere hundred miles from Madinah Shareef. Such would be the dominance of kuffaar during that era.
The Muslims would also be under severe persecution and oppression from the Khaleefah of that time and they will have no place to run.
The Ahle Bait (Family of Nabi Muhammad Sallallahu alayhi wasallam) will experience difficulties and persecution.
Throughout the world earthquakes would occur frequently. Innocent people will be put to death. A man by the name of Haarith Harraath will emerge from beyond the Euphrates river, and before him will be another by the name of Mansoor. The former (i.e. Haarith) will be preparing the minds of Muslims to-accept Imam Mahdi when he comes. He will perform the same task for Imam Mahdi, what the Quraish performed for Rasulullah (Sallallahu alayhi wasallam) in Madinah before Hijrat. Mansoor will aid him in this direction.
It is wajib upon every Muslim to help this Haarith, or to respond to his call.
The Abdaals and pious leaders will all be on the lookout for Imam Mahdi, knowing that only he could bring relief to the failing Ummat.
There will be a fight in Makkah between three people, each one being the son of a Khaleefah, over leadership of the Muslims. However, none of them will gain the Khilafat. This fight will take place in the month of Zul-Qa'dah, and even in Mina during Hajj, there will be quarrelling. All this will occur in the same year as Imam Mahdi's election.
An army will come from the East towards Arabia. The East here refers to Khurasan, i.e.northeastern Iran, which includes the borders of the Soviet Union and Afghanistan. They will pave the way for the establishment of Imam Mahdi's kingdom. This army will carry black banners. Nothing shall stop their onward march, and eventually they will plant their flag on the soils of Jerusalem.
This army will seek the leadership of Arabia. The current leader will refuse to hand over theKhilafat.
A tremendously fierce battle will ensue, the likes of which Muslims had never yet experienced. The army from Khurasan will be victorious and will eventually be granted the leadership.