Stephen Tvrtko I (Serbo-Croatian: Stjepan Tvrtko, Стефан Твртко; c. 1338 – 10 March 1391) was the first of the kings of Bosnia and widely considered one of the country's greatest medieval rulers. A member of the House of Kotromanić, Tvrtko succeeded his uncle Stephen II as Ban of Bosnia in 1353. He ascended as a minor and at first reigned under the regencies of his father, Vladislav, and then of his mother, Jelena. Early in his reign Tvrtko quarreled with Roman Catholic clergy, but later enjoyed cordial relations with all religious communities in his realm. After initial difficulties – the loss of large parts of Bosnia to his overlord, King Louis I of Hungary, and brief deposition by magnates – Tvrtko's power grew considerably. He conquered the remnants of the neighbouring Serbian Empire i