Abu Muhammad Hasan bin Ali (peace be upon him) (232-260 A.H.), nicknamed Askari, Naqi, Zaki, Fadel and Amin, is the son of Imam Ali Hadi (peace be upon him), the father of Hazrat Mahdi (may God bless him and grant him peace), and the eleventh leader of the Shiites.

After the martyrdom of his father, he reached the Imamate at the age of 22 and was the Imamate of the Shiites for 6 years. His Imamate was under the strict control of the Abbasid caliphs, but with all the continuous pressures and efforts of the Abbasid government, he carried out a series of political, social and scientific activities in order to preserve Islam and fight against anti-Islamic thoughts. Defending Islam and rejecting doubts and training prominent students, expanding the circle of communication with Shiites through representatives, leading secret political activities, raising political awareness about important Shiite men, providing financial support to Shiites, introducing Hazrat Mahdi (peace be upon him) as his successor, preparing Shiites for the time of occultation and other cases were among the activities of that Imam.

Finally, on the 8th of Rabi al-Awwal 260, Imam Hassan was poisoned and martyred by the order of Motamed Abbasi, and was buried in the same city of Samarra next to his father's grave.