Jadwiga of Poland
In 1386, Grand Duke Jogaila of Lithuania was baptised into Christianity and married Queen Jadwiga of Poland, taking the name Władysław II Jagiełło and becoming King of Poland. This created a personal union between the two countries and a potentially formidable opponent for the Teutonic Knights. The Order initially managed to play Jogaila and his cousin Vytautas against each other, but this strategy failed when Vytautas began to suspect that the Order was planning to annex parts of his territory.