Marwān ibn al-Ḥakam ibn Abiʾl-ʿAs ibn Umayya (Arabic: مروان بن الحكم بن ابو العاص بن أمية‎‎), commonly known as Marwan I (ca. 623–626 — April/May 685) was the fourth caliph of the Umayyad Caliphate, ruling for less than a year in 684–685, and founder of its Marwanid ruling house, which remained in power until 750. Marwan had known the Islamic prophet Muhammad and is thus considered a sahaba (companion). He served as the secretary and right-hand man of his kinsman Caliph Uthman (r. 644–656) and participated in the defense of his house during a rebel siege. Uthman was, nonetheless, assassinated by the rebels, prompting Marwan to kill Talha ibn Ubayd Allah, whom he held culpable, during the Battle of the Camel in 656. He gave allegiance to Caliph Ali (r. 656–661) and later served as governor of Medina under his kinsman Caliph Mu'awiya I (r. 661–680), founder of the Umayyad Caliphate.

Marwan led the Banu Umayya clan in the Hejaz, and when Mu'awiya I's successors Yazid I and Mu'awiya II died in 683 and 684, respectively, he organized the defense of the Umayyad realm in the Hejaz against Abd Allah ibn al-Zubayr, a rival claimant to the caliphate. Ibn al-Zubayr expelled Marwan and his clan from Medina, and they became refugees in Syria. As he was prepared to pay allegiance to Ibn al-Zubayr, his kinsman, Ubayd Allah ibn Ziyad, urged him to instead volunteer his candidacy for the caliphate during a summit of loyalist tribes at Jabiya. The tribal nobility, led by Ibn Bahdal of the Banu Kalb, ultimately elected Marwan and together they defeated the pro-Zubayrid Qaysi tribes at the Battle of Marj Rahit.

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