Abdullah bin Masud is one of the prominent figures in the history of early Islam. He is a reciter of the Quran and has his own copy of this holy book. The assessment of his personality is of interest since the Islamic schools of thought confirm his familiarity with the sciences of the Quran, hadith, recitation and interpretation. His performance before the martyrdom of the Prophet (p.b.u.h.) as a follower of the revelation school and after his demise as a defender of Islam is of concern. Bin Masud is among the Companions who clearly expressed his views recurrently during his lifetime even if this practice and following the school of the truth apparently harmed his social position. This outspokenness makes an independent school out of Abdullah bin Masud’s thoughts and this school made a foundation for the activities of Imam Ali (a.s.) during the time of his apparent rule in Kufa. His cooperation, mainly in the field of cultural activities, with the second Caliph, on the one hand, and his outspoken stance against the performance of the three caliphs after the Prophet (p.b.u.h.), especially Osman, on the other, has been evaluated differently by different people. However, as he was permitted by Imam Ali (a.s.) to cooperate with the caliphate, his general performance can be considered positive and the only serious criticism levelled against him from Ahl al-Beyt (a.s.) in different resources is his omission of the last two chapters of the Quran from his copy of this holy book. Hence, other accusations brought against him can be justified on the grounds that he defended Imam Ali (a.s.).