Bishop Martin III (Johannis) of Medininkai is the first Žemaitijan ordinary of whose activities we know more than merely a few facts. Unfortunately most of what is written about him is false: he did not have a surname (Lintfari is a scribal error for Lituani); he did not hold canonries in Liège, Louvain or Poznań, let alone ‘work’ in Flanders or Poland. This article reviews diverse known sources for Martin’s life and career and provides new information from the Gniezno Consistory Court record and other manuscripts which reveals how his career formed in the Roman Curia before he returned to Lithuania as bishop of Medininkai and reflects his concerns for the affairs of Church and State. An appendix provides five new sources from manuscripts in Cracow and Gniezno along with a new edition of Martin’s will from the earliest surviving copy.