Tamīm al-Dārī was one of the Prophet Muḥammad's companions and an early convert to Islam from Christianity. His name is most closely associated with the eschatological traditions concerning the Dajjāl (the Muslim Antichrist), and various early ascetic ideas. The best known story involving him is in fact his meeting with the Dajjāl, after he and others of his tribe are shipwrecked on a mysterious island. He is taken by a creature called al-jassāsa to meet a chained man in a monastery, who asks the tribesmen a number of questions about the state of the outside world, most of which are related to the area of the Rift Valley in Syria. After they answer him, he proclaims himself to be the Dajjāl and announces that he is about to be let loose on the world. Somehow Tamīm and his companions manage to leave the island and come to visit the Prophet, who hears their story and relates it to the populace of Medina. However, in spite of this story, historical material about him, as is common with the Prophet's companions in general, is hard to come by. In this article I will explore some of the historical traditions connected with this figure and try to establish which material is reliable and which is not.