This article surveys the diasporic life and legacy of the Ethiopian ecclesiastic Täsfa Ṣeyon. After examining his origins in the Christian kingdom of Ethiopia and the circumstances of his arrival in mid-sixteenth-century Rome, the article outlines his contributions to the evolving Latin Catholic understanding of Ethiopia. Täsfa Ṣeyon was a librarian, copyist, teacher, translator, author, and community leader, as well as a prominent adviser to European humanist scholars and Church authorities concerned with orientalist philologia sacra as it pertained to Ethiopian Orthodox (täwaḥedo) Christianity. As such, he was a key extra-European agent in the Tridentine project of Ethiopianist and Eastern Christian knowledge production. The article also surveys the complex modern legacy of Täsfa Ṣeyon's career, documenting his posthumous influence in the fields of Ethiopianist Semitic studies and Ethiopian vernacular historiography.