He became the fourth Sunni caliph...

He became the fourth Sunni caliph, the last of the "Rightly-Guided Caliphs", after the death of 'Uthman. He was finally assassinated by followers of the Khawarij (an early schismatic sect), after five years as caliph. He is buried in Najaf in Iraq. The Second Imam, al-Hasan The Second Imam, al-Hasan (3/62 -50/670) He was the elder son of 'Ali by the Prophet's daughter Fatimah.

He laid claim to the caliphate for some six months after the death of his father, but was finally forced to surrender it to Mu'awiyah. For the rest of his life he lived in Medina in seclusion. He is buried in the Baq'i cemetery in Medina. The Third Imam, al-Husayn The Third Imam, al-Husayn (4/62 -6I/680) The younger son of 'Ali by Fatimah, like his brother he lived most of his life quietly in Medina under the watchful eyes of the caliph's officials and spies.

When Mu'awiyah's son Yazid became caliph, he demanded allegiance from al-Husayn, who refused to give it. Finally al-Husayn felt it necessary to go into battle against Yazid to protest against the injustices which were being carried out in the name of Islam. He and a small group of followers including most of his immediate family were cruelly massacred at Karbala.

The day of his martyrdom (" 'Ashura ") has become the most solemn day of the Shi'ite calendar, marked by processions and universal mourning. Its celebration symbolizes the whole ethos of Shi'ism. He is buried in Karbala in Iraq.

The Fourth Imam, 'Ali Zayn al-'Abidin The Fourth Imam, 'Ali, known as Zayn al-'Abidin and al-Sajjad (38/65895/7I2) The son of Imam al-Husayn by the daughter of Yazdigird, the last Sassanid king of Iran, he was not able to carry arms at Karbala because of illness, and thus he was saved the fate of his three brothers. For most of his life he lived in seclusion in Medina, having contact with only a few select followers.

His piety-which is reflected in his collected prayers, al-Sahifat al-sajjadiyyah -is proverbial. He is buried in the Baqi' cemetery in Medina. The Fifth Imam, Muhammad al-Baqir The Fifth Imam, Muhammad, known as al-Baqir (57/675II4/732) The son of the fourth Imam, he was present at Karbala at a young age.

Because of changing political and religious conditions, among them the general revulsion following the events at Karbala, many people came to Medina to learn the religious and spiritual sciences from him.