Marwan II was the last Caliph of the Ummayyad Dynasty, and was the grandson of Marwan I. Before becoming Caliph in 744, he was the governor of Armenia. He conquered Syria in 746. In 750, he was killed in a battle at the great Zab River by the Abbasids, Iranians and Iraqis. This battle destroyed the Ummayyad Dynasty. Marwan II was killed in Egypt six months later. Marwan II was also known as al Himar (the ass) for his strength.
Further Reading:
The Caliphate: Its Rise, Decline, and Fall - From Original Sources