Frederick II (December 26, 1194 – December 13, 1250), Holy Roman Emperor of the Hohenstaufen dynasty, was pretender to the title of King of the Romans from 1212, unopposed holder of that monarchy from 1215, and Holy Roman Emperor from 1220 until his death in 1250. He was also King of Sicily, from 1198 to 1250, where he was raised and lived most of his life (his mother, Constance of Sicily, was the daughter of Roger II of Sicily). He is also referred to as Frederick I of Sicily. His empire was frequently at war with the Papal States, so it is not surprising that he was excommunicated twice. Pope Gregory IX went so far as to call him the anti-Christ. After his death the idea of his second coming where he would rule a 1000-year reich took hold, possibly in part because of this.

Said to speak nine languages and be literate in seven [Armstrong 2001, p. 415] (at a time when many monarchs and nobles were not literate at all), Frederick was a very modern ruler for his times, being a patron of science and learning (astronomy and astrology, also: one of his advisors was the famous astrologer Guido Bonatti from Forlì) and having fairly advanced views on economics. He abolished state monopolies, internal tolls, and import regulations within his empire.

He was patron of the Sicilian School of poetry, where in his royal court in Palermo, from around 1220 to his death, we witness the first use of a literary form of an Italo-Romance language, Sicilian. The poetry that emanated from the school predates the use of the Tuscan idiom as the preferred lingua franca of the Italian peninsula by at least a century. The school and its poetry were well known to Dante and his peers and had a significant influence on the literary form of what was eventually to become the modern Italian.

He was known in his own time as the Stupor mundi ("wonder of the world"). Frederick wrote, or rewrote, a manual on the art of falconry, De arte venandi cum avibus ("On the art of hunting with birds"), of which many illustrated copies survive from the 13th and 14th centuries.

Frederick II was considered singular among the European Christian monarchs of the Middle Ages. This was observed even in his own time, although many of his contemporaries, because of his lifelong interest in Islam saw in him "the Hammer of Christianity", or at the very least a dissenter from Christendom. Many modern medievalists view this as false, and hold that Frederick understood himself as a Christian monarch in the sense of a Byzantine emperor, thus as God's Viceroy on earth. Other scholars view him as holding all religion in contempt, citing his rationalism and penchant for blasphemy. Whatever his personal feelings toward religion were, certainly submission to the pope did not enter into the matter. This was in line with the Hohenstaufen Kaiseridee: the ideology, claiming the Holy Roman Emperor to be the legitimate successor to the Roman emperors.

Modern treatments of Frederick vary from sober evaluation (Stürner) to hero worship (Ernst Kantorowicz). However, all in all, agreement prevails over the special significance of Frederick II as Holy Roman Emperor, even if some of his actions (such as his politics with respect to Germany) remain quite dubious.

Children
• With Constance of Aragon:
• Henry (VII) of Germany
• With Yolande of Jerusalem:
• unnamed daughter, died young
• Conrad IV of Germany
• With Isabella of England:
• Margaret of Sicily, margravine of Meissen
• Henry Charlote of Sicily
• Frederick of Sicily
• Carl Otto of Sicily
• With Bianca Lancia:
• Manfred of Sicily
• Constance (Anna) of Sicily, married John III Ducas Vatatzes
• Violante of Sicily, married Riccardo di Caserta
• With Adelheid Enzio:
• Enzio of Sardinia
• With Richina of Wolfs'oden:
• Margaret of Swabia
• With Matilda of Antioch:
• Frederich of Antioch
• With unknown:
• Selvaggia
• Conrad of Antioch
• Richard of Theate
• Catarina of Marano
• Blanchefleur
• Gerhard
• Frederick of Pettorana