Cousin and son in law of the Prophet Muhammad, and the fourth caliph. `Ali was elected caliph following the murder of `Uthman, but he did not punish `Uthman's murderers, thus apparently favoring the Medinans over `Uthman's Meccan family. The Prophet's wife `Aisha attempted unsuccessfully to overthrow `Ali. Mu`awiya, a Meccan relative of `Uthman, also claimed the caliphate. An arbitration in 657 favored Mu`awiya, and some of `Ali's followers (the Kharijites) condemned him for submitting to the arbitration. A Kharijite murdered `Ali in 661. He is regarded by Shi`ites as by right the direct successor of Muhammad, whose authority was then transmitted to a succession of Imams.