Stephen Tvrtko I was the first king of Bosnia. A member of the House of Kotromanic, he succeeded his uncle Stephen II as Ban of Bosnia in 1353. As he was a minor at the time, Tvrtko's father, Vladislav, briefly ruled as regent, followed by Tvrtko's mother, Jelena.
He conquered some remnants of the neighbouring Serbian Empire in 1373, after the death of its last ruler and his distant relative, Uros the Weak. In 1377, he had himself crowned king of Bosnia and of Serbia, claiming to be the heir of Serbia's extinct Nemanjic dynasty.
Tvrtko I is considered one of the greatest medieval rulers of Bosnia, having "left behind a country larger, stronger, politically more influential and militarily more capable than the one he inherited." His political achievements were aided by the feudal anarchy in Serbia and Croatia, while the Ottomans were still not close enough to seriously threaten him. The Bosnian economy flourished, new settlements and trade centres appeared, and his subjects' living standards improved.
Depicted above is Tvrtko's coin, featuring fleur-de-lis and his coat of arms.
Image Source: Wikipedia.org