Ilkhanid era chronicles of Juvayni (d. 1283), Rashid al-Din (d. 1318) and Kashani (d. ca 1337) record three very different narratives of Hasan-i Sabbah’s (r. 1090-1124) conversion to Ismailism. One of these accounts embedded in the story of the famed “three school fellows” is found only in the work of the last two historians. This story brought together the wazir Nizam al-Mulk (d. 1092), the poet Omar Khayyam (d. 1131) and Hasan-i Sabbah in a childhood pact of blood brothers that the successful one amongst them would aid the others and that a betrayal of this by the Nizam led Hasan to convert to Ismailism. This paper examines the different layers in each of the conversion narratives and what they add to the biography, perhaps the hagiography, of the founder of the Nizari Ismaili polity in Iran (fl. 1090-1256). A new analysis of the “three school fellows” story - previously believed to be spurious - suggests its purpose, dating and the nature of the original Nizari source. It also sheds fresh light on the factionalism among the Nizaris and their relationships with the equally fractious Saljuqs in a period of immense tumult, shifting alliances and brutal conflict.