The present study provides an analysis of an important Shi'ite personality, Mitham b. Yahya al-Tammar, a close follower and confidant of 'Ali b. Abi Talib, who played a significant role in the early history of Shi'ism but has been quite ignored by modem scholarship. We hope to redress the matter here, and provide insight into his biography, his relations with 'Ali, and how these relations enriched early Shi'ite thought and religious jurisprudence. In the following pages we shall discuss Mitham's origins, his personality, his descendants and the role they played in Shi'ite jurisprudence, his commentary on the Qur'an and his other writings, his role as transmitter of traditions, his students, his mystical knowledge, and the events surrounding his death.