The Prophet's uncle who lost his life in the Battle of Badr was Hamzah. Hamzah was the brother of the Prophet's father and a strong supporter of Islam. During the Battle of Badr, he fought bravely but was eventually killed by an enemy soldier named Wahshi. Hamzah's death was a great loss to the Prophet and the Muslim community, as he was not only a close relative but also a powerful defender of the faith.