Ali

Ali is the point where Islam divides, and the division is about events, not doctrine, which is why it has never been argued away.

He is the Prophet's cousin, raised in his household, married to his daughter Fatima, and father of Hasan and Husayn. Both Sunni and Shia tradition agree on all of that, and on his being among the earliest to accept the message. They diverge on what happened in 632.

Sunni tradition holds that the community gathered at Saqifa after the death and gave allegiance to Abu Bakr, that this was a legitimate consultation, and that Ali eventually accepted it and became the fourth of the Rightly Guided Caliphs. Shia tradition holds that the Prophet had already designated Ali at Ghadir Khumm, on the return from the farewell pilgrimage, taking his hand and saying that whoever holds me as his master holds Ali as his master. The event at Ghadir Khumm is reported in Sunni collections too, including chains Sunni scholars accept; the dispute is about what the word rendered master means. Shia read it as authority and designation. Sunni read it as friendship and support.

So this is not a case of one side inventing an episode. Both accept the report. They read one Arabic word differently, and a fifth of the world's Muslims stands on each side of the reading.

Ali became caliph in 656 after the murder of Uthman, faced civil war, and was killed in 661 at Kufa by a member of a faction that had abandoned him for accepting arbitration.

The best-known text under his name is the Nahj al-Balagha, the Peak of Eloquence, a collection of sermons, letters and sayings compiled by al-Sharif al-Radi around the year 1000, roughly three and a half centuries after Ali's death. It is a work of extraordinary literary power and is central to Shia devotional and intellectual life. Its authenticity has been questioned since the medieval period, initially by Sunni critics and later in Western scholarship, on the grounds of the gap in transmission, the absence of chains for many pieces, and stylistic features that some argue belong to a later Arabic. Shia scholarship has defended it in detail. The honest description is that the compilation is tenth-century, that some material within it is attested earlier and independently, and that the collection as a whole cannot be traced to him.

Ali also stands at the head of nearly every Sufi initiatory chain, including in orders that are entirely Sunni. This is easy to misread as a Shia connection; it is not. Sufism traces esoteric knowledge through him because of his closeness to the Prophet, and the great majority of Sufi orders are Sunni.

At the far edge, some groups took veneration of him past what either main tradition accepts. The Alawites of Syria and the Alevis of Anatolia hold positions about him that Sunni and Twelver Shia authorities have both, at various times, rejected. These are distinct communities with distinct histories, and lumping them together is a common error.