This King Founded a Short-Lived Empire During the Middle Ages

On September 8, 1331, Stefan Dušan declared himself king of Serbia. An excerpt from the article:

"Stefan Dusan, also known as Stefan Uros IV, is one of the most important people in Serbian history. He was the King of Serbia from 1331 to 1346 and he founded the short-lived Serbian Dynasty in 1346. He ruled as the Emperor of the Serbs, Greeks, and Albanians until his death in 1355. Although he was an exceptional commander, much of Dusan’s success was based on opportunism. He displayed an uncanny ability to take advantage of a situation when it presented itself."