The Imam after the commander of the faithful, Hazrat-e Ali, Peace be upon him, was his son, Al-Hassan, the son of Fatima, Daughter of Mohammad, the Lord of Messengers, May God bless him and his pure family.
His epithet was Abu Mohammad and he was born in Medina in the month of Ramadhan three years after Hijra (624 A.H.). At the age of 7, the infallible Imam (AS) lost his honorable grandfather, Hazrat-e Mohammad (p.b.u.h) and his holy mother, Hazrat-e Fatima (SA).
When Hazrat-e Ali (AS) was martyred, Imam Hassan (AS) was bequeathed to imamate by Allah.
When Mu'awiyah abi Sufyan, an irresistible enemy of Imam Ali and his pure family (AS), learnt of the people's pledge of allegiance to Imam Hassan (AS), he coveted the caliphate and set off towards Iraq, the Imam Hassan's (AS) seat of government and the flight started.
On the other hand, Mu'awiyah deceived all commanders of Imam Hassan's (AS) army with deceitful hopes and money and incited the army and Imam's followers to revolt against him.
Therefore Imam Hassan (AS) was made to accept the peace proposed by Mu'awiyah and left the authority of the government to him (of course they bounded after Mu'awiyah's death, the caliphate would be returned to Imam Hassan (AS) and his Shi'ite family .
Meanwhile Mu'awiyah entered Iraq. In a public address, Mu'awiyah revoked all the peace terms. After that Mu'awiyah arrested and tortured the Shi'ite and the Household of the Prophet Mohammad (p.b.u.h). During this period Imam Hassan (AS) lived without any security and safety at his home and was finally martyred in 50 A.H. by his wife who was urged to poison him by Mu'awiyah.
Imam Hassan (AS) was the most similar person to the Apostle of God, Hazrat-e Mohammad, May God bless him and his pure family, in appearance, manner and nobility.
The infallible Imam was buried in the Baqi' Cemetery.
There are several narrations that the Holy prophet (AS) has stated:
"Hassan and Hossein are my two (grand) sons."
source : www.sibtayn.com