Frederick II of Sicily (1194-1250) has crossed the path of this blog more than once, but has not yet been featured.
He declared the Edict of Salerno, separating physicians and pharmacists.
Frederick was interested in math and science, and was friendly to and supportive of Fibonacci.
He promised to go on the Fifth Crusade, mentioned here, but never participated; he was blamed for its failures by Christians all over Europe as well as Pope Honorius III (who had been Frederick's tutor while young).
From the time he was declared Holy Roman Emperor in 1220 until his death 30 years later, he was a tremendous influence on science and culture, but a difficulty for popes and religion—odd, considering he willingly took the title Holy Roman Emperor. Although Pope Innocent III was his guardian growing up, Frederick often said blasphemous things, supposedly mocking Moses and Jesus and Mohammed for being frauds. His public attitude toward religion was unusual for his era and position, and Dante's Inferno places him in the circle of hell reserved for heretics.
He was, however, also possessed of a rationalism that was unusual for his era. He hired Arabs/Muslims as soldiers and personal guards; he hired Jewish scholars to be at his court. He pointed out the unfairness of trials by ordeal, because the stronger man would always win regardless of guilt or innocence. He hired the mathematician and scholar Michael Scot (of whom Honorius III thought very highly) to, among other things, make new translations of Aristotle and Arabian works into Latin. Michael Scot's translation of Aristotle was done with the help of Hermannus Alemannus ("Herman the German").
He had three wives and several mistresses. His third wife was Isabella of England, the daughter of King John Lackland. It was a political marriage, taken on because marrying an English princess would make his political opponents lose support from England. Once Isabella arrived in Sicily, she was sent to live in seclusion in Padua with only two of her English retainers.
Although Frederick had a profound and positive impact on laws and science, his personal manner made him many enemies and detractors. The Hohenstaufen lineage, which had included Frederick Barbarossa, lost power after Frederick II's death.