Usman ibn Sayeed
Usman ibn Sayeed (260 A.D. - 304 A.H.) .  He was the holder of the office in the time of Imam Ali an-Naqi and Imam Hasan al-Askari and both these Imams considered him as their private secretary and treasurer, and they both considered him thoroughly reliable.  What he said on their behalf was the same as if they had said it.  At times Imam Hasan al-askari addressed him in public as the "agent for the property of Allah".  For which property he was to give a receipt when he accepted it on behalf of the Imam.  Upon the death of Imam Hasan al-Askari, he acted as the chief deputy of Imam Mahdi (a.t.f.s.)  This office he served till his death in Baghdad in 304 A.H.  His grave is a the Shari-al-Maydan, in the mosque near the city gate.  In 408 A.H. there was an entrance to the tomb room from a small door in the prayer niche of the mosque, but thirty-two years later this wall was destroyed and the tomb was left in the open court where it could be visited by anyone.