Jadwiga was King of Poland from 1384 to 1399. Even though she was a woman, her title was King, to reflect that she held the title in her own right.
She became monarch through yet another dynasty that wasn’t willing to lose power just because they couldn’t produce sons. Her father was Louis, King of Hungary and Poland, (and much of eastern Europe at times). When the previous King of Poland (Casimir the Great) had died without a suitable son to take the throne, the throne was transferred to Louis, and his mother Elizabeth, Casimir’s sister. The Poles didn’t much like the idea of sharing a monarch, so on Louis’ death, after a couple of years of argument, Hungary got Louis’ older daughter, and Poland got his younger daughter, Jadwiga. She was 11 when she was crowned.
She married Grand Duke Jogaila of Poland, which was a manipulation from the Lords who were actually running Poland, with the aim of combining Lithuania and Poland. So she didn’t have much actual power, with the Lords of Poland and her husband doing most of the actual ruling. She is most known for giving most of her personal wealth away to charities, and for reforming the Krakow academy, now known as the Jagiellonian University, and one of the oldest universities in Europe.
She died in childbirth at the age of 26, and afterwards was venerated in Poland as a saint, mainly for her charitable works. Her tomb in Krakow’s Wawel cathedral has been the site of reputed miracles over the years.
She seems to have been mostly a dynastic pawn, rather than wielding power for herself. But nevertheless, she is still remembered strongly in Poland, 600 years after she died. Her power may have been soft power, in the current jargon, but she used it to found a University. That’s an achievement worth being remembered for.