Polish king, John Casimir, is the ruler of Poland during the most of the seriest, or at least, first major installments.
Born in 1609, he was crowned in 1648 and abdicated in 1668, so since our series begin in 1655 and continue all the way to 1668 and further, he will become a prominent figure, tho he won't show up on the pages of novels, comics, or on the screen too frequently, being a rather controversial figure.
Well, he wan't very liked by his polish subjects, even hated, to the point where a lot of Poles - both nobility and soldiers - decided to become loyal to the swedish king, when he invaved the country.
Therefore, John Casimir, had to flee, he found an asylum in the neutral Austrian Empire, where he was hiding for a short period of time, but then returned and took power and the polish throne, once again.