Answer:
This Hungarian king is Sigismund of Luxembourg (1368-1437). He was crowned king of Hungary and Croatia in 1387. Also he was crowned as Emperor of the Holy Roman Empire in 1433 until his death.
He lead a crusade against the Ottomans in the siege of Niccopolis near the Black Sea. The objective was to save the Byzantine Empire and Bulgaria from the Ottoman rule.
The battle of Niccopolis was fought between 25 and 28 September, 1396. There the Sultan Bayezid I defeated the Christian army, which have soldiers from France, England, Germany, Bulgaria among other armies.
He is also remembered for be the founder of the Order of the Dragon, with the objective to defend Europe from the Turkish. Among others its most known member was Vlad Tepes, also known as Dracula.
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