Erik Magnusson, king of Sweden (b. 1339)
Eric XII (Swedish: Erik Magnusson; 1339 – 21 June 1359) was King of Sweden and lord of Scania in 1344–1359. He was

a co-ruler with his father, King Magnus IV, from 1356 until his death in 1359. Referring to Erik Magnusson as King Eric XII is a later invention, counting backwards from Eric XIV (1560–68). He and his brother Charles IX (1604–1611) adopted numerals according to a fictitious history of Sweden. The number of Swedish monarchs named Eric before Eric XIV (at least seven) is unknown, going back into prehistory. It would be speculative to try to affix a mathematically accurate one to this king.