The great warrior and companion Hazrat (Ra) was an uncle of the Prophet Muhammad(pbuh). He is also a son of Abdulmuttalib bn Hashim. And he is a brother to the Noble Prophet (pbuh) through breastfeeding.
His conversion to Islam was a sudden incident.
After being bestowed with Prophethood, the Prophet Muhammad (pbuh) started preaching Islam publicly. For this reason the infidels started opposition and oppression. In the meantime one day the Prophet Muhammad (pbuh) was in meditation at the foot of Safa mountain. The wicked Abu Jahl rebuked him in an extremely, objectionable language and struck him. Uttering not a word the Prophet Muhammad(pbuh) returned home.
Hamza (Ra) had just returned from hunting. He came to know about this incdent. He rushed angrily in that condition to the compound of Ka'aba. Seeing Abu Jahl sitting among other leaders of Quraish he roared like a lion. Striking Abu Jahl’s head with his bow again and again, he said, what you dare rebuke my nephew and strike him. Hamza declared.
So listen I recite LA ILAHA ILLAL LAH, MUHAMMAD RASULULLAH. and I accept islam, the religion of Muhammad (pbuh). Hamza went to the Noble Prophet Muhammad (pbuh) and narrated the whole incident. He also informed him about his conversion to Islam. The Prophet Muhammad(pbuh) was very pleased by acceptance of Islam by a warrior like Hamza.
Hazrat hamza (Ra) was a mighty brave warrior. He was honoured by the title of the lion of Allah and his Prophet’s. for his incomparable bravery.
After accepting islam hamza (Ra) dedicated himself to the cause of the Prophet Muhammad(pbuh) and Islam. He remained like a shadow with the Prophet Muhammad (pbuh) during different crises. When the Prophet Muhammad (pbuh) was engaged in preaching Islam security of the Prophet Muhammad (pbuh) and the Muslims rested with Hamza (Ra).
Hazrat Hamza (Ra) earned name and fame for his excellent bravery in the battle of Badr. In that battle the Muslims killed many Quraish leaders including Abu Jahl.
In the battle of Uhud, Hamza (Ra) was one of the targets of the infidels for killing, because many Quraish heroes were killed by Hamza (Ra) in the battle of Badr. As a result at one stage of the battle, an Abyssinian slave wahshi Ibn Harb with a spear attacked him. He fell down on the ground and was martyred.
The Noble prophet (pbuh) was very grieved by the death of Hamza. because of this, all the Sahabas mourned for him.
And on the day of Judgment, Hamza will be raised as the leader of all martyrs.
May Allah(Swt) be pleased with him.