Abdullah Ali al-Asghar (680 - 742) was a prominent figure in early Islamic history, and the fourth Caliph according to the traditional numbering. He was the third son of Hussein ibn Ali, and thereby a grandson of the first Caliph, Ali, and a great-grandson of the Prophet Muhammad.
At the time of Asghar's birth, Arabia was in a fragile truce between the supporters of the sons of Ali and the supporters of the Umayyad family, who had murdered Ali and usurped the caliphship. Ten years before, Asghar's uncle Hassan had agreed a treaty with the Umayyad caliph Muawiyah ibn Abu Sufyan, whereby Muawiyah's successor would be chosen not by him but by a shura council. After Hassan's death however the treaty was broken, and Muawiyah appointed his own son Yazid as successor.
When Asghar was only two weeks old, Muawiyah died and Yazid proclaimed himself caliph. Hussein and his supporters disputed this and began travelling to Mecca to organize a rebellion. Before they could go far, however, their party was ambushed by Umayyad troops and Hussein and almost all his family were killed. Asghar was the only survivor, having been sent in secret to Axum as a precaution against such a disaster.
These events caused outrage not just in Arab lands but also in the wider Muslim world. Romania and Axum both declared war on the Umayyads and began preparing for an invasion of Arabia. Yazid was soon defeated and executed, and Asghar was proclaimed Caliph.
However, Asghar was by this time still less than two years old, so preparations were made for a regency. After much debate, it was decided that all of the Arab clans should be involved in governance in order to avoid such a situation occurring again, and so the Arab Republic was created in order to govern the region until Asghar came of age. Meanwhile, the religious duties of the caliphship would be performed by Emperor Constantine IV, while Axumite troops would be responsible for keeping the peace in Yemen and the Hejaz. Asghar himself was to be raised by his cousin, Hassan al-Mu'thanna.
In 695 Ali al-Asghar was proclaimed to be of age and fit to assume his duties. He requested, however, that his regents continue ruling in his stead for some time until he had reached full maturity.
In 698 Asghar gathered together his family and advisors and informed them of his wishes. He did not desire to be ruler of the Arabs or of the Muslim world, instead preferring to devote his life to religion and scholarship. Having observed the successes and failures of the last eighteen years, and noting how well the Muslim world seemed to have coped, he asked that the institutions of the Arab Republic be made permanent so that it could rule Arabia indefinitely, and bequeathed the religious duties of the Caliph to the Roman Emperor, Tiberius III, and his successors.
Having issued the relevant proclamations, and allaying the fears of the many who tried to dissuade him from this course, Asghar entered the madrasa at the Prophet's Mosque and studied and taught there for the next forty years.
In 638 Asghar, feeling he had no more to offer, resolved to travel abroad to learn more. His journeys eventually brought him to Constantinople, where he was an honoured guest of Leo III and Constantine V. There he died in 642, leaving behind several children.