Imam Hasan's [a] role, during the lifetime of his father, and especially under his caliphate, was marked by his total obedience to his father, who was his example and leader. He dealt with him, not only as a kind son, but also as an obedient soldier in the deepest sense of the word, with its implications of compliance and discipline. The role of Imam Hasan [a] was expressed, during all the critical days his father, Imam Ali [a], lived through, in total submission to his father, his leader and the source of his inspiration.
Following are some of his deeds during this part of his life:
As soon as he entered Kufa, the multitudes swelled around Imam Hasan [a] declaring their loyalty and their readiness to help him. He made a speech, in which he blew enthusiasm into their inept souls, and urged the people to hoist the banner of jihad high. Imam Hasan [a] was most successful in accomplishing his mission. He exhorted them to support the right, defend the message and its noble state.
In the meantime, Imam Hasan [a] was standing amid the masses calling them to rally around the truth. In one of his speeches he said:
"Thanks be to Allah. There is no god other than He. He has no partner. I praise Him and He is praiseworthy. Allah gave you great favours and showered you with His graces which are beyond number. One cannot possibly thank Him for them. Neither a statement nor saying can express them. We are angry only on behalf of Allah. He favoured us with what cannot be given by anyone but Him. We should, therefore, thank Him for His bounties, tribulations and favours. Our praise should ascend to Allah, carrying our satisfaction to Him. It should be truthful. Our praise has to be so true that Allah believes us. It has to make us entitled to receive more of his bounties. Our praise should increase rather than decrease Allah's favours. No group of people gather around some matter without making it firmer, and their beliefs solid. So mobilize yourselves for the fight against your enemy, Mu'awiyah, and his soldiers, because he has advanced against you. And do not discourage one another, for discouragement cuts asunder the heartstrings. Advancing under the spearheads is a sign of bravery and piety, for no people had ever observed jihad without the lifting of malaise from among them by Allah. He would spare them the tribulations of humility, and guide them to the hallmarks of denomination..."
In this speech, Imam Hasan's [a] aim was to solidify the bonds of unity, close the ranks of the people, and rally the people to challenge the party led by Mu'awiyah and a handful of opportunists.
"Stand up, son, and talk about these two men: Abdullah bin Qais, and Amru bin al-Aas," Imam Ali [a] told his son.
Imam Hasan [a] stood and addressed the people, telling them the real dimensions of the situation. He said:
"O people! You have talked too much about these two men. They were only chosen to judge according to the Book and in the light of its guidance. But, they judged according to their whims and not the Book. This being true, their verdict cannot be called a judgement. Rather, it was an opinion forced upon them. Abdullah bin Qais erred when he named Abdullah bin Umar as the caliph. He made mistakes concerning three points: First, he disagreed with his father who did not rate him as qualified for caliphate, nor did he appoint him as member of the Shura (consultative group). Secondly, he did not consult him on the matter. And thirdly, neither the immigrants nor the Ansar (helpers) rallied around him. These are those who appoint the ruler and establish his reign over the people. As for arbitration, the Messenger of Allah [s] himself had chosen Sa'd bin Ma'ath for this. And he did judge with what pleases Allah. Undoubtedly, if he had deviated, the Messenger of Allah [s] would not have approved of him".
In these words, the grandson of the Holy Prophet [s], Imam Hasan [a], clarified the matter, disclosed the falsity of the arbitration, and proved to the people the mistake of Abu Musa al-Ash'ari, who was elected by the common people among the army of Imam Ali [a], and without thinking it over, they charged him with a task he could not fairly accomplish. The man had bad intentions.
Imam Hasan [a] demonstrated some or Abu Musa's mistakes. Among them was deposing Imam Ali [a] and calling Abdullah bin Umar bin al-Khattab the caliph of Muslims. His judgement involved three errors, not to mention the rest of his arbitration. Imam Hasan [a] was an astute thinker, had a sound foundation in logic and politics. His analysis of Abu Musa's actions in the arbitration process was acute and left no doubt in a reasonable mind that the analysis was without flaw. He said that:
Moreover, Imam Hasan [a] set an example of a just and good arbitration, which is approved of by Allah. He cited the arbitration of S'ad bin Ma'ath, who was chosen by the Messenger of Allah [s], to settle the question of Bani Quraidhah, after their military defeat by the Messenger of Allah [s]. His judgement was firm and sound.
 Baqir Sharif al-Qarashi, Hayat al-Imam Hasan [a], (Najaf:1965). vol.1, p.387.
 Ibid., p.432.
 Abdullah bin Qais Abu-Musa al-Ash'ari.
 Ibid., p. 479.