Muawiyah I

Mu'awiya and his father had opposed Muhammad until Mecca fell in 630; afterward he became one of the prophet's scribes. Appointed a deputy commander in Syria's conquest, he rose to governor under Caliph Uthman and built power through alliances with local tribes and command of campaigns against Byzantium. When Uthman was assassinated in 656, Mu'awiya refused to recognize Ali's succession and the two fought to a stalemate at Siffin in 657. After Ali's murder in 661, Mu'awiya forced Ali's son Hasan to abdicate and secured control of the caliphate. He established administrative departments, led near-annual raids on Constantinople, and launched the conquest of North Africa under Uqba ibn Nafi in 670. By naming his son Yazid as successor, he broke with precedent and set the caliphate on a hereditary path - a move that sparked the Second Fitna after his death in 680.