In August 1927 British colonial authorities arrested Hamman Yaji, Emir of Madagali, an infamous slave trader who terrorized the neighboring montagnard population of northern Nigeria and the ruling colonial administration. They seized his diary, which soon became a fabled document in northern Nigerian history. Written in Arabic and translated into English by a British colonial official, the diary chronicles Hamman Yaji's activities between 1912 and 1927. He recorded what he did each dayÑwhere he traveled, his slaving raids and slave-trading activities, visitors and gifts received, his relations with friends and family and with the British administration, and his practice of Islam.The diary, made accessible to scholars for the first time since its composition more than 75 years ago, is enhanced by a substantial introduction that places Hamman Yaji in historical and cultural perspective and describes the diary's discovery, translation, and significance for British colonial and West African history.