ALI, IBN ABI TALIB. — Cousin and son-in-law of Muḥammad, and his fourth successor as head of the Muslim community; the last of the series of "orthodox" or "rightly guided" caliphs (Rāshidūn). Son of Abū Ṭālib, Muḥammad’s uncle, he was considerably younger than the Prophet. He was among the first to embrace Islam, and his ties with Muḥammad were strengthened when he married the Prophet’s daughter Fāṭimah, by whom he had two sons, al-Ḥasan and al-Ḥusayn, progenitors of all subsequent, real or alleged, descendants of the Prophet.
'Ali faithfully assisted his cousin in the difficult early years of the Meccan mission, followed him to Medina at the hijrah, and distinguished himself for military valor in the battles and expeditions of the first decade. He does not, however, appear—despite the assertions of tendentious Shiite tradition—to have enjoyed any special influence with the Prophet, perhaps because of his limited political sense and his temperament, brave in battle but irresolute. Under the caliphate of the third caliph, 'Uthmān, 'Ali became the leader of the opposition, composed of pietistic elements (the so-called Qurrā', "reciters" of the Qur'an), Medinese Muslims hostile to the long-pagan Umayyad family to which 'Uthmān belonged, and turbulent rebels. In the disorders that culminated in 656 with the assassination of 'Uthmān, 'Ali played an ambiguous role that compromised him morally before the hostile Umayyad faction, when he found himself the beneficiary of the caliph’s murder by succeeding him.
As soon as he came to power, he encountered opposition from other early companions of the Prophet, such as Ṭalḥah and al-Zubayr, backed by Muḥammad’s widow, 'Ā'ishah. Victorious over them in the so-called Battle of the Camel (November 656), 'Ali had to face an even graver danger in the Umayyad counteroffensive led by the governor of Syria, Mu'āwiyah ibn Abī Sufyān, who rose under the slogan "vengeance for 'Uthmān." When attempts at reconciliation failed, 'Ali marched against Mu'āwiyah and clashed with his army at Ṣiffīn on the right bank of the middle Euphrates. The battle, which seemed to favor 'Ali, was suspended due to the clever appeal of Mu'āwiyah’s partisans for arbitration "according to the Qur'an" (as they ambiguously expressed it). His political career was obstructed and ultimately destroyed by the fanatical Kharijite movement, which he defeated at the Battle of Nahrawān without, however, managing to uproot it—a movement that for about a century would foment bloody rebellions and unrest within the Muslim community.
'Ali, from whom Mu'āwiyah had wrested Syria and Egypt, fell victim in January 661 to a Kharijite assassin in the mosque of Kūfah, which he had made his capital from the outset. Mu'āwiyah was recognized by all as caliph, inaugurating the Umayyad dynasty, while 'Ali’s descendants, first and foremost his two sons, were left with no choice but to renounce all political ambition (as the elder, al-Ḥasan, did) or resort to conspiracy and futile insurrection, as was the fate of the younger, al-Ḥusayn, twenty years later, when his rebellion was bloodily suppressed.
Entirely disproportionate to 'Ali’s historical role, his mediocre character, and the failure of his life is the importance his figure assumed in the later evolution of Islam. Considered by Sunnis as a wise and valiant right hand of the Prophet, he was regarded by Shiites as the Prophet’s sole legitimate successor in the leadership of the Muslim community and even in the prerogatives of prophetic inspiration and infallibility. This conception, in the most extreme Shiite currents, culminates in a virtual deification of 'Ali, placed even above Muḥammad himself and regarded as the supreme earthly incarnation of the divine logos. It can be said that, apart from the Kharijites—who had long since virtually disappeared—all heterodox Islam revolves around the veneration of 'Ali and the transformation of his historical figure. Even in the Christian West, his figure has been known alongside that of Muḥammad; and Dante placed 'Ali (the accentuation does not correspond to the Arabic form of the name, being due to Turkish pronunciation) in the circle of sowers of scandal and schism, with a dim awareness of the complications that within Islam itself stem from this disconcerting and tragic figure.