As we are aware, occultation is of two types: the Minor Occultation and the Major Occultation with the former being the foundation for the latter.
Imam Hasan al-Askari (a.s.) was martyred in 260 A.H., within 5 years of the birth of Imam al-Mahdi (a.t.f.s.) in 255 A.H. Immediately after his martyrdom, the soldiers of the Abbassid Caliph surrounded his house. They were in search of his son, who was his successor.
These historical incidents in themselves are a proof of the danger to the life of Imam Hasan al-Askari’s (a.s.) son. Occultation was thus necessary for the protection of Imam Mahdi’s (a.t.f.s.) life and for the continuity of the institution of Imamat and successorship of prophethood.
The Holy Prophet (s.a.w.s.) had already prophesied about this:

ثُمَّ يَغِيْبُ عَنْهُمْ اِمَامُهُمْ مَآ شَآءَ اللهُ وَ يَكُوْنُ لَه غَيْبَتَانِ…

‘Then till Allah desires, their Imam will be hidden from them and he will have two occultations...’[1]

Selection of the Special Representatives
Subsequent to the martyrdom of Imam Hasan al-Askari (a.s.), the Shias were enveloped in the darkness of doubt and indecision. The demise of Imam (a.s.) was not the sole reason for their condition, essentially it was also due to the political situation prevailing at that time.
The atmosphere of fear and anxiety unleashed by the Abbassid Caliphs on the Shias and the lack of direct contact with the Imam (a.s.) aggravated things further. Soon the Shias disintegrated into different sects.
The martyrdom of Imam Hasan al-Askari (a.s.) disturbed the Shias even more. The situation worsened to such an extent that many Shias despaired of their faith. Such conditions marked the beginning of the minor occultation. Imam az-Zaman (a.s.) was physically absent from the midst of the people.
To ensure his safety and well-being, Imam Hasan al-Askari (a.s.) had not introduced him to everyone, but only to the innermost circle of his Shias. In the words of Shaykh Mufid (a.r.), ‘To the extent that he [Imam Hasan al-Askari (a.s.)] had not introduced his son to a large group of his followers’.[2]
However, it was not as if Imam Hasan al-Askari (a.s.) had not introduced his son and successor at all. The introduction was made, but only to the trustworthy ones. Ahmad b. Ishaaq al-Qummi was informed through a letter. He was instructed to inform reliable people about the birth of Imam Mahdi (a.t.f.s.). Also, care was taken to ensure that this news did not break out to the general masses.

Some Incidents
(i) Some descendants of Janabe Abu Talib (a.s.) stayed in Medina. They were true believers, having complete faith that the son of Imam Hasan al-Askari (a.s.) would be the twelfth Imam. However, after the martyrdom of Imam Hasan al-Askari (a.s.) some of them turned apostates (i.e. they turned away from Shiaism).[3]
(Although they were Shias of Hazrat Ali (a.s.), they deviated after the demise of Imam Hasan al-Askari (a.s.))
(ii) Muhammad b. Ibrahim was confused after the martyrdom of the eleventh Imam (a.s.). This was despite the fact that his father Ibrahim b. Mahziyar was a representative of Hazrat Wali al-’Asr (a.s.) in Ahwaz. Sheikh Kulaini (a.r.) narrates that when the father of Muhammad b. Ibrahim died, some amount of Khums (Sihm ul-Imam) was in his possession.
His father had mentioned in his will that he should be careful about the Sihm ul-Imam and it should reach to the correct person. In a state of confusion, Muhammad b. Ibrahim carried the money to Iraq. He decided to hand over the amount only after a satisfying proof was presented to him.
Later, a messenger came to his house and advanced some convincing signs about the money and took custody of it. Muhammad b. Ibrahim became distressed and few days had not passed when he received a letter appointing him as a representative in his father’s place.[4]
(iii) Sheikh Saduq (a.r.) narrates from Abu Raje Misri, ‘Two years after the demise of Imam Hasan al-Askari (a.s.), I undertook a journey to search for his successor but I failed in my mission. In the third year while I was still seeking Imam Hasan al-Askari’s (a.s.) successor in Medina, Abu Ghanim invited me to his house one evening.
At that time, a thought crossed my mind that if at all there was any son of Imam (a.s.) then after three years he would definitely have made himself known. Suddenly a voice reached my ears, ‘O Nasr b. Abdullah (Abu Raje), ask the Egyptians whether they have seen the Prophets (a.s.) in whom they believe?’ Abu Raje says, ‘Till then I was unaware of my father’s name as I was born in Madyan and Naufali had brought me to Egypt. After my father’s death I was brought up in Egypt. Listening to this I got up. Instead of going to Abu Ghanim’s place I took the road to Egypt.[5]
(iv) Hasan b. Abdul Majid says, ‘I was in doubt about Hajiz b. Yazid (he was one of the representatives of Imam az-Zaman (a.t.f.s.) in Baghdad and among the foremost assistants of ‘Uthman b. Sa’eed (r.a.)). Then I collected some money and reached Saamarrah. There I received a letter stating, “It is not proper to doubt about us or about those who are helpers in our affairs. Whatever you have brought with you, deposit it in the custody of Hajiz b. Yazid’.[6]
There are many such incidents in the books of traditions. Nevertheless, such doubts and confusions led to the disintegration of Shiaism into many sects. Al-Ma’sudi in ‘Muroojuz Zahab’ mentions about twenty such sects. Sa’d Qummi in ‘Al Maqaalaat wal Feraq’ has mentioned 15 such sects. While Nawbakhti in ‘Firaq ‘ush-Shia’ and Sheikh Mufid (a.r.) in ‘Fusool-ul-Mukhtaar’ have named fourteen sects each. Shahrastani in ‘Al Milal wa al-Nahal’ has mentioned eleven sects.
It is famous among the scholars that after the demise of Imam Hasan al-Askari (a.s.), the Imamites (Shias) were divided into fourteen sects and according to the contemporary ulema these 14 sects from the aspect of beliefs, form 5 sects.
Currently, only the Imamiyyah sect (believers in the Imamat of Imam Mahdi (a.s.)), among all others, has survived.

Reminder
We observe that despite the foresight and anticipation of the Shias of that time, they were afflicted with doubt and skepticism. Imam az-Zaman (a.t.f.s.), who never forgets his Shias has himself declared: “We are neither negligent of your affairs nor are we forgetful of your remembrance. If it was not so, calamities would have surrounded you and enemies would have crushed you.”
Surely, if it wasn’t for the link between the noble and extraordinary Shias and Imam az-Zaman (a.t.f.s.), the entire foundation of Shiaism would have been decimated.
To avoid such a scenario, in the initial period of occultation, Imam az-Zaman (a.s.) maintained contact with the Shias through the special representatives. The common people were thus trained to live without an apparent Imam for a long period. This contact satisfied the people who were denied even a glance of their leader.

The Important Role of the Representatives
The leadership of the four special representatives transformed the conditions of the Shias for the better. The Shias were saved from disintegration and deviation. Of course, this was possible only with the guidance of Imam az-Zaman (a.s.).
The era of the first representative was marked with the presence of many groups having variant views vis-a-vis the son of Imam Hasan al-Askari (a.s.). However, the era of the second representative witnessed a successful transition, as his teachings prevailed among the Shias, thereby weakening the other groups.
Consequently, at the time of the third and the fourth representatives, the new generation of Shias had become acquainted with the true Shiite beliefs. They considered the words of the special representatives as the words of Imam az-Zaman (a.t.f.s.) himself and they were desirous of meeting him.

Same Signature in Every Tawqee’
The belief of the new generation was strengthened by the presence of the same signature in all the letters issued to the four representatives. The fourth (and last) special representative was issued the last letter, which announced the termination of the minor occultation and the onset of the major occultation. The foundation of the major occultation of Imam az-Zaman (a.s.) was laid with the help of the minor occultation.
Under these circumstances the Shias were united. Shaykh Mufid (a.r.) in 373 A.H. while writing the book, ‘Al Fusool-ul-Mukhtaarah’ records that out of the fourteen sects only the Imamiyyah sect survived. He further writes that this sect had the maximum number of scholars, visionaries, righteous ones, worshippers, jurists, traditionalists, linguists and poets. As these personalities were the leaders and were highly revered in society, the Shia Imamiyyah led an honourable existence.[7]

Purpose of Representation
Representation had two basic objectives:
(i) Mentally preparing the masses for the major occultation and gradually habituating them to live in the period of occultation. At the same time they had to safeguard the people from any negligence towards the matter of occultation. Had Imam (a.t.f.s.) directly gone into occultation, people would have denied his very existence and would have deviated. The special representatives of Imam az-Zaman (a.t.f.s.) in the minor occultation prepared the people mentally for the major occultation.
(ii) Guiding the lovers and followers of Imam az-Zaman (a.s.) and protecting the unity of the Shia community. To a certain extent the special representatives filled the void created by the occultation of Imam (a.t.f.s.). Through them, Imam (a.t.f.s.) guided his Shias and ensured that no adversity touched them in his absence.
The deviation that would have occurred without the special representation is unimaginable.
Lastly, let us discuss some of the general responsibilities of the special representatives:

a) Concealing the abode of Imam Mahdi (a.t.f.s.)
This responsibility involved two facets. The dwelling of Imam (a.t.f.s.) was to be concealed not only from the enemies but also from the Shias. They prohibited their local representatives from even mentioning the name of Imam (a.t.f.s.) among the general masses. The Shias were thus protected from the Abbassides.
On the other hand they were also responsible for proving the existence of Imam (a.t.f.s.) among the reliable Shias to prevent any doubt from creeping in their beliefs. In some instances they even arranged meetings or indicated a place for meeting Imam (a.t.f.s.) to reliable people so as to disperse the cloud of uncertainty.
We shall further enlighten our readers about the responsibilities of the special representatives in the brief life-sketch of the second representative, Janab Muhammad b. ‘Uthman Ibn Sa’eed (a.r.). Insha-Allah.

b) Preventing the disintegration among the Shias:
We have mentioned this point in some detail in the preceding paragraphs.

c) Resolving the religious and legal problems and explaining beliefs and knowledge:
They were the channels for presenting religious and legal problems of the Shias before Imam (a.t.f.s.) and conveying Imam’s (a.t.f.s.) reply to the people. One can find a number of questions and their replies during the time of the second representative.

d) Contending the false claimants of Mahdaviyat:
This too will be discussed Insha-Allah in detail in the life history of the second representative.

e) The collection and distribution of the wealth of Imam (a.t.f.s.):
The special representatives collected the share of Imam (a.t.f.s.) from the Shias and their own local representatives. It was then presented to Imam (a.t.f.s.) and expended according to his (a.s.) instructions.

f) Appointing local representatives
The practice of appointing local representatives was prevalent since the time of the previous Imams (a.s.). This practice continued during the occultation of Imam Mahdi (a.t.f.s.). The local representatives were appointed by the special representatives.
Sometimes the local representatives got the opportunity to meet Imam (a.t.f.s.) along with the special representatives. Some local representatives got the honor of meeting Imam (a.t.f.s.) once, while others got this grace several times. The second special representative had ten local representatives in Baghdad. The highest among them was Janab Husain b. Rauh (a.r.) who later went on to become the third special representative.
We now proceed with the details of the life histories of the special representatives.

Notes:
[1] Bihar al-Anwar, Vol. 52, Pg. 380
[2] Kitabul Irshad, pg. 345
[3] Al-Kaafi, vol. 2, Kitab al-Hujjah, Chapter of Birth of Sahebuz Zaman (a.t.f.s.)
[4] Ibid., Vol.2, Pg. 456
[5] Kamaaluddin, by Shaykh Saduq, vol.2, pg. 491, chap. 25, tradition 15
[6] Al-Kafi, vol. 2, Chapter of birth of Imam (a.s.)
[7] Peeramun Zindagi al-Nawwaab al-Khassa al-Imam al-Zaman (a.s.), p. 84