A king with this name captured Visby when he invaded Gotland, but had to leave Henning Podebusk to negotiate with an alliance that included the Confederation of (*) Cologne.  
A ruler with this name spent his early reign furiously buying back land lost by his insolvent father, Christopher II. Legendarily, a red cloth with a white cross on it fell from the heavens to inspire another king with this name to win the Battle of Lyndanisse at modern-day Tallinn. A king with this name captured Visby when he invaded Gotland, but had to leave Henning Podebusk to negotiate with an alliance that included the Confederation of (*) Cologne.  A ruler with this name compiled the Code of Jutland, while another man, the rival of Albert of Mecklenberg, was the father of Margaret I, who founded the Kalmar Union. A king with this name known as "Atterdag" was indifferent to petitions over fishing rights, resulting in him pissing off a mercantile alliance that forced him to sign the Treaty of Stralsund. For 10 points, the fourth Danish king to have what name was defeated by a rising Hanseatic League?
A ruler with this name spent his early reign furiously buying back land lost by his insolvent father, Christopher II.
Valdemar [number or epithet does not matter]