Nasir al-Din Tusi completed his Nasirean Ethics (Akhlaq-i Nasiri), the most highly esteemed book on ethics in Persian, around the year 633 AH / 1235 CE while in the service of the Ismaili governor of Quhistan. Two decades later, Tusi parted company with the Ismailis. This essay charts the course of his works, in particular Nasirean Ethics to his enigmatic treatise on Sufi ethics entitled The Attributes of the Illustrious (Awsaf al-ashraf). Prof. Madelung investigates Tusi’s sources, putting a number of what he views as erroneous suppositions about the man to rest. This study of Tusi’s works and philosophy affords the reader an insight into Tusi’s own personal journey from the time he penned Nasirean Ethics (Akhlaq-i Nasiri) to his eventual status as King of Philosophers by the end of his life.