Stephen Tvrtko I (1338 – 10 March 1391) was
Ban of Bosnia from 1353 until his
coronation in 1377 and
King of Bosnia thereafter. He also claimed the title King of Serbs from 1377 and the title
King of Croatia after 1390. A member of the Bosnian
Kotromanic dynasty which had ruled the
Banate of Bosnia, he was a "politically adept and religiously tolerant ruler" and under his command Bosnia reached its peak and became the strongest power in the
Balkans, conquering parts of what is today Serbia, Croatia and Montenegro.