Osman ibn Affan, the third caliph
On July 17, 656 AD, Osman ibn Affan, the third caliph, was killed by a group of Muslims dissatisfied with his 12-year rule, during which, in addition to rampant nepotism that saw his kinsmen take charge of key posts and openly violate every law of Islam, some of the most prominent companions of Prophet Mohammad (SAWA), such as Abu Zarr Ghaffari and Ammar ibn Yasser, were mistreated. When he became caliph, his kinsman, the notorious Abu Sufyan had advised him to rotate the caliphate amongst the Omayyads.
Osman thus reconfirmed Abu Sufyan's dubious son Mu'awiyya as governor of the vast Syrian Province (made up of present day Syria, Jordan, Lebanon, and Palestine); appointed his own step-brother Walid bin Uqba – an open sinner and son of the Prophet's sworn enemy Uqbah ibn Abu Mu'ayit – as governor of Kufa; his foster brother, Abdullah ibn Sa‘d ibn Abi as-Sarh who had apostatized in the Prophet's lifetime, as governor of Egypt; and Abdullah bin Amer as governor of Basra.
In the capital Medina, virtual power of the entire realm was vested in Osman's cousin and son-in-law, Marwan ibn al-Hakam (who along with his father had been expelled by the Prophet for mocking Islam). The resulting tyranny and hoarding of wealth by the ruling elite despite their military conquests in the east and the west, reached such alarming proportions that Ayesha, the daughter of Abu Bakr and one of the wives the Prophet had married in the last ten years of his life, branded Osman an apostate and called for his blood.
There were complaints from all quarters and matters deteriorated when the Egyptian petitioners sensed betrayal from Osman against them, especially after discovery of a secret letter ordering the governor of Egypt to put to death their leaders, especially the pious Mohammad bin Abu Bakr, the son of the first caliph.
The several hundred Egyptian Muslims rushed to Medina, besieged the caliph's house for several days, and finally burst inside and killed him, despite the earnest efforts of Imam Ali (AS) to mediate and avoid bloodshed. They then refused to allow the burial of Osman in Baqie, the graveyard of the Muslims. He was finally buried in the adjacent Jewish graveyard. Decades later, the Omayyad rulers demolished the wall separating the two cemeteries and merged the Jewish cemetery into the Muslim one to ensure that the grave of their kinsman was inside a Muslim cemetery.