Born Aqa Buzurg-i-Nishapuri, the son of a devoted Babi, he was later given the title Badi' (unique, wonderful) by Baha’u’llah. Reputed to be a wild, unruly youth, he had no interest in his father's affairs until, during the visit to his home of a traveling teacher, Mulla Muhammadi-Zarandi (Nabil-i-A'zam), he listened to some verses from a long poem by Baha’u’llah and was so entranced that he devoted the balance of his life to serving Him. After his conversion he set out to visit Him, traveling on foot from Mosul to 'Akka. It was during this visit that he was chosen to deliver a letter (Tablet) from Baha’u’llah to Nasiri'd-Din Shah . (The A to Z of the Baha’i Faith by Hugh Adamson)
Shoghi Effendi describes these events in the following passage:
Aqa Buzurg of Khurasan, the illustrious "Badi" (Wonderful); converted to the Faith by Nabil; surnamed the "Pride of Martyrs"; the seventeen year old bearer of the Tablet addressed to Nisiri'd-Din Shah; in whom, as affirmed by Baha’u’llah, "the spirit of might and power was breathed," was arrested, branded for three successive days, his head beaten to a pulp with the butt of a rifle, after which his body was thrown into a pit and earth and stones heaped upon it. After visiting Baha’u’llah in the barracks, during the second year of His confinement, he had arisen with amazing alacrity to carry that Tablet, alone and on foot, to Tihran and deliver it into the hands of the sovereign. A four months' journey had taken him to that city, and, after passing three days in fasting and vigilance, he had met the Shah proceeding on a hunting expedition to Shimiran. He had calmly and respectfully approached His Majesty, calling out, "O King! I have come to thee from Sheba with a weighty message"; whereupon at the Sovereign's order, the Tablet was taken from him and delivered to the mujtahids of Tihran who were commanded to reply to that Epistle - a command which they evaded, recommending instead that the messenger should be put to death. That Tablet was subsequently forwarded by the Shah to the Persian Ambassador in Constantinople, in the hope that its perusal by the Sultan's ministers might serve to further inflame their animosity. For a space of three years Baha'u'llah continued to extol in His writings the heroism of that youth, characterizing the references made by Him to that sublime sacrifice as the "salt of My Tablets."
(Shoghi Effendi, 'God Passes By')