Answer
Mu'awiya was appointed as the governor of Syria during the reign of Caliph Uthman, who was the third caliph of the Rashidun Caliphate. Mu'awiya was a member of the Umayyad clan, which was one of the most powerful clans in Arabia at the time. He was a skilled military commander and administrator, and he played a key role in the expansion of the Umayyad Caliphate.