Kazimierz IV the Short:
1102 - 1144
Duke of Prussia: 1125 -1144
Duke of Samogitia: 1131 - 1144
King of Poland: 1144
Kazimierz IV the Short was a successful Duke of Prussia for almost 20 years before his election as King of Poland in the summer of 1144. He expanded his Duchy into Samogitia and even claimed the title for himself after the capture of Zhmud. His nickname, 'the Short', refers to his short stature, although it is sometimes used condescendingly to refer to his 4-day rule as king. He is often said to have been "good for Prussia, bad for Poland", and this is a mostly true statement- while his death was the immediate beginning of the Great Polish Succession Crisis, his son (later Kazimierz V of Poland) was personally trained by him and would save Poland from its crisis.
There is no doubt he was good for Prussia; during his rule he expanded into Samogitia, historically Lithuanian territory. He was a zealous knight, ready to fight off the predominantly Lithuanian pagans. In two wars, he and a few other Polish dukes defeated the rapidly-expanding and powerful Kingdom of Lithuania, seriously curbing any attempts at westward expansion by the pagan Queen. Instead, she expanded east and south, creating a massive pagan state in between Poland and Rus. This expansion, at its height reaching to Novgorod in the north, the Crimea to the south, and the Volga to the east, would shape the course of eastern European history forever.
Kazimierz IV of Poland was born in Malbork, in present-day Prussia. His father was Kazimierz II of Prussia, a descendant of Wladyslaw I of Mazovia, who was Boleslaw III's brother. Thus, he was closely related to the ruling Piast branch and was seen as a valid successor when he came of age. He was not that intelligent as a boy, but his honesty was admired by his father and he was extremely zealous. Later on he was noted to be an ambitious man and desired to expand Prussia to the east. He became Duke of Prussia in 1125, at the age of 23, and only 2 years later began the Prussian-Lithuanian War: a war against the burgeoning pagan Kingdom of Lithuania for the realm of Samogitia, which constituted Memel, Scalovia, and Zhmud.
The deciding turn in the battle was the Battle of Samland Forest- around 3000 Lithuanian troops were ambushed by a much smaller Prussian force (of around 1000) in forests surrounding Sambia. The battle was extremely one-sided; the Lithuanian forces, composed of a combination of Polish mercenary cavalry and Lithuanian peasant levies, fell apart quickly when the two groups could not distinguish the other. In the confusion, Prussian forces were able to cut down almost the entire Lithuanian contingent at the cost of almost nothing- historical records indicate perhaps less than 100 soldiers loyal to the Duchy of Prussia were killed. Although Kazimierz IV lost use of one of his legs in the battle, it was an impressive victory that disparaged the Lithuanians and caused them to surrender quickly.
Left to right: The Battle of Samland Forest; here, Polish mercenaries fighting for Lithuania are attacked by Lithuanian pikemen; the general confusion in the forest caused many friendly casualties for the Lithuanians. Comparably, the skirmish-focused and organized Poles were able to devastate the Lithuanians with arrow fire, a modern portrait of Kazimierz IV
Acquiring these territories was seen as a great boon to Prussia and Poland and he was rewarded personally by king Kazimierz III. Becoming very popular against the nobles of Poland due to his contributions against the enemy pagans, he was chosen as the elected successor to the crown sometime around 1135. When king Kazimierz III died in 1144, the message was sent to Malbork that Kazimierz III of Prussia was to become Kazimierz IV of Poland. The day after the message was recieved, Kazimierz IV passed away. The Duke of Gdansk, Sczcepan I, who had befriended Kazimierz, then claimed the throne for himself. As Sczcepan could claim the crown of Poland but not Prussia or the former crown demesne, the Great Polish Succession Crisis had thus began.