They were the faithful friends, helpers and companions of Imam Hussein (A.S). Some were old like Habib ibn Madhahir; others like Wahab al Kalbi were young. Some were noblemen like Zuhayr ibn Qayn, others like Jawn bin Huwai were slaves. Some like Salim and Amir came from towns like Kufa and Basra; others had lived in the desert. There were men like Ammar and Muslim ibn Awsaja, who had been with the Prophet (P.B.U.H&H.P) and Nafi and Jundab, who were friends of Imam Ali (A.S). They were all killed fighting bravely against the army of Umar ibn Saad, defending Islam on the day of Ashura and the Imam (A.S) wept for each of them.
Ref: Shia books for children