Zawisza Czarny z Garbowa (Zawisza the Black of Garbów, also known as The Black Knight; c. 1379 in Stary Garbów, Poland – 1428 in Golubac, Serbia), Sulima Coat of Arms, was a famous Polish mediæval knight and diplomat.
Zawisza Czarny was a famous Polish knight, winner of many tournaments, a symbol of a knight and a model of all knightly virtues. His father was Biernat from Garbów, mother is unknown. His nickname certainly comes from his appearance and not like later believed from a black armor, which is currently located in the armory of Jasna Góra Monastery. He was apparently dark haired and had a dark complexion.
Zawisza became for many Poles one of the most popular folks heroes thank to his exceptional bravery and proverbial reliability and loyalty. Famous is the Polish saying: "Polegać na nim jak na Zawiszy" (Rely on him like on Zawisza). This motto also became part of the Polish Scouts oath.
A monument to Zawisza Czarny in Golubac fortress, Serbia, has the inscription: "In Golubac, his life was taken by the Turks in 1428, the famous Polish knight, the symbol of courage and honor, Zawisza the Black. Glory to the hero!"
Zawisza was a winner of many tournaments. Probably, at the time, he had no match among Western knights.
Looks like I had the first correct answer. What of King Jan III Sobieski, some said he was.
Yes, Jan III Sobieski was a great warrior but primarily he is famous for being the king, not the knight. Besides, he lived in times when there weren`t knights anymore. They belong to the Middle Ages while Sobieski belongs to Modern Times.