
Jagiełło was actually the Grand Duke of Lithuania (and therefore Lithuanian) prior to converting to Christianity, marrying Queen Jadwiga of Poland, and thus becoming the King of Poland. He lead a untied Poland and Lithuania against the Teutonic Order which resulted in the decisive victory at the Battle of Grunwald in 1410. Interestingly enough there is a statue of King Jagiełło in Central Park in NYC. Here is a sweet 360 degree view of it.

There is a dragon wrapped around the King's feet on his tomb because he was a member of the Order of the Dragon. The tomb at Malbork is merely a replica of the real thing which is located at Wawel Cathedral in Kraków.