Hamza is the Prophet's uncle, the son of Abdul Mutalib and so the brother of the Prophet's father.
He was a brave warrior and a strong man who sought his own pleasures and never cared about the issues of Mekkah.
One day after a hunting trip, a Muslim woman asked him "how he could go hunting while his nephew was assaulted by Abu-Jahl."
Hamza was enraged and headed to the Ka3ba and asked Abu-jahl, "How dare you abuse him?" and then he hit him on the head.
The next day Hamza went to his nephew the Prophet PBUH and Mohammed proposed Islam to his uncle and Hamza embraced it without any hesitation. He encouraged the Prophet to proceed with his message and promised him he'll always be by his side.
Unlike Hamza, Omar embraced Islam in a gradual process. He used to be an extremely tough person. He used to walk after the prophet PBUH wherever he went, and used to prevent him from talking to people and spreading the message of Islam.
Omar tells the story of his Islam. He says that the first time Islam found a way to his heart was when he used to beat up his female slave. Strong as he was, he would beat her until he would get tired, yet she remained quite unexhausted. Once again, a Muslim woman demonstrated her strength and capability to fortify the society.
Another day, Omar went to meet his drinking friends as usual, but he did not find them. Nor did he find the wine seller. He decided to go to the Ka3ba. When he arrived he found the prophet PBUH praying. He decided to listen quietly and see what he said. The Prophet PBUH was reading Surat Al-Haqqah.
click to listen to Surat Al-Haqqah: