Died in 1266

Jan 11 Swietopelk II Duke of Pomerania Duke of Pomerelia-Gdańsk from 1215 until his death. He was a son of Mestwin I and the first member of the Samborides to style himself dux
Feb 26 Manfred King of Sicily the King of Sicily from 1258 to 1266. He was a natural son of the emperor Frederick II of Hohenstaufen but his mother, Bianca Lancia , is reported by Matthew of Paris to have been married to the emperor while on her deathbed
Mar 17 Peter of Montereau a French architect. He is widely recognized as one of the most important proponents of Gothic architecture, though little is known of his life and sources vary as to which buildings are by him
Apr 4 John I Margrave of Brandenburg from 1220 until his death Margrave of Brandenburg, jointly with his brother Otto III "the Pious".
Aug 4 Odo Count of Nevers Count of Nevers and Auxerre and the heir of Hugh IV, Duke of Burgundy. His mother was Yolande of Dreux
Oct 21 Birger Jarl a Swedish statesman, Jarl of Sweden and a member of the House of Bjelbo, who played a pivotal role in the consolidation of Sweden. Birger also led the Second Swedish Crusade, which established Swedish rule in Finland. Additionally, he is traditionally attributed to have founded the Swedish capital, Stockholm around 1250. Birger used the Latin title of Dux Sweorum which in English equals Duke of Sweden, and the design of his coronet combined those used by continental European and English dukes
Oct 28 Arsenije Sremac the second archbishop of the Serbian Orthodox Church and a disciple of Saint Sava of Serbia.
Oct 29 Margaret of Austria Queen of Bohemia a Queen Consort of the Romans 1225–35, titular Duchess of Austria in 1252–60, and Queen consort of Bohemia 1253–60.
Dec 3 Henry III the White a Duke of Wrocław from 1248 until his death.