Short answers, pulled from the story.
Shia Islam is the second-largest branch of Islam, rooted in the belief that Muhammad designated his cousin and son-in-law Ali ibn Abi Talib as his rightful successor and divinely guided imam. Shia Muslims revere the ahl al-bayt, the purified family of Muhammad, as infallible inheritors of his spiritual authority. They hold that leadership of the Muslim community should come from this family line.
Shia Muslims number roughly 200 to 260 million people as of 2026, an estimated 10 to 13 percent of the world's Muslim population. They form a majority in Iran, Iraq, and Azerbaijan, and make up nearly half the citizen population of Bahrain.
The split traces to the succession after Muhammad's death in 632, when a meeting at Saqifa elected Abu Bakr as caliph while Ali and the Prophet's relatives were occupied with the funeral. Shia Muslims regarded this as a violation of Muhammad's designation of Ali at Ghadir Khumm. The Battle of Karbala in 680 and the martyrdom of Husayn ibn Ali are widely cited as the definitive moment of separation between the two sects.
At the Battle of Karbala in 680, Husayn ibn Ali, grandson of Muhammad, was intercepted by the army of Yazid after refusing to swear allegiance to him. Husayn and approximately 72 of his family members and followers were killed, and Husayn's head was delivered to Yazid in Damascus. The Shia regard Husayn as a martyr, and his death is commemorated each year on the Day of Ashura.
The three principal branches of Shia Islam are Twelverism, Ismailism, and Zaydism. Twelvers are the largest branch and believe in twelve divinely ordained Imams. Ismailis, known as Seveners, follow Ismail ibn Jafar, and Zaydis, sometimes called Fivers, recognize Zayd ibn Ali as their fifth Imam.
In Shia Islam, Imam Mahdi is the prophesied eschatological redeemer who will rule before the Day of Judgment and rid the world of evil. Twelver Shia Muslims believe the twelfth Imam, Hujjat Allah al-Mahdi, is already on Earth in Occultation and will return at the end of time. His coming is said to coincide with the Second Coming of Jesus, who will descend east of Damascus to fight the Masih ad-Dajjal.
Divine justice, called adl, is one of the five foundations of religion in Twelver Shia doctrine, alongside monotheism, prophethood, imamate, and resurrection. It holds that God cannot act unjustly because injustice is incompatible with His essential nature, and that the human intellect can independently recognize that justice is good and injustice evil. This rationalist position makes the intellect, aql, one of the four sources of Jafari jurisprudence.