Hasan al Askari was born in Samarra to Ali al-Hadi and Saleel. Hasan would live almost his entire life under house arrest in Samarra. His title al-Askari derives from the Arabic word asker which means Army. Hasan's title was reflective of his living most of his life in a garrison town.
Despite being confined to house arrest for almost his entire life, Hasan al-Askari was able to teach others about Islam, and even compiled a commentary on the Quran that would be used by later scholars. Despite his confinement as a prisoner, he was ocassionally allowed to go to Baghdad, although it was under guard, and he was able to marry a Byzantine slave woman who according to some traditions was a granddaughter of a Roman emperor. Her name was Nargis.
Hasan would die at the young age of 27 on January 4, 874, apparently he was poisoned. He left only one son, Muhammad al-Mahdi who was five at the time of Hasan's death. Hasan's funeral was attended by many people, including the Abbasid caliph Al-Mu'tamid. According to some traditions, Hasan's brother Jafar was getting ready to lead the funeral prayer when, Hasan's son came out and told his uncle “set aside uncle, only an Imam can lead the funeral prayer of an Imam” [1]. Upon which Jafar stepped aside, and the prayer was led by the five-year old, after which the child returned to his house. After returning to his house, he was never seen again, eluding the Abbasids who were sent to find him. His disappearance indicates that he is the Hidden Imam, and the Shia believe he will return at the end of time.
Hasan al-Askari is buried next to his father in Sammara, their mausoleum is an important site for Shia Muslims.