According to legend, Masoud was an infamous black slave belonging to the Fatimid Caliph Al-Hakim bi-Amr Allah. He was said to be a large man used by Hakim to carry out a bizarre punishment. Al-Hakim was said to have occasionally wandered the streets of Cairo looking for deceptive merchants. When he discovered one, he would immediately have Masoud publicly sodomise the man.
This folk tale has inspired a phrase which has survived into modern times, in which citizens of Cairo threaten to "bring Masoud" to a merchant who they believe is trying to cheat them. There are a number of tales of questionable historicity portraying Al-Hakim as deranged. Ismailis claim that anti-Ismaili historians concocted derogatory stories about him. Among these is the legend of Masoud.