The greatest Medival King

I vote for Frederick II Hohenstaufen.

From wikipedia:

Personality

In Frederick II we encounter one of the most remarkable personalities in world history. His contemporaries called him stupor mundi, the "wonder" � or, more precisely, the "astonishment" � "of the world"; the majority of his contemporaries, subscribing to medieval religious orthodoxy, under which the doctrines promulgated by the Church were supposed to be uniform and universal, were, indeed astonished � not seldom repelled � by the highly developed individual consciousness of the Hohenstaufen emperor, his temperamental stubbornness and his unorthodox, nearly unstoppable thirst for knowledge.

Frederick II was a religious sceptic. He is said to have denounced Moses, Jesus, and Muhammad as all being frauds and deceivers of mankind. He delighted in uttering blasphemies and making mocking remarks directed toward Christian sacraments and beliefs. Frederick's religious scepticism was most unusual for the era in which he lived, and to his contemporaries, highly shocking and scandalous. In his period in Jerusalem, this behaviour was much to the dislike of the Muslims too, who grew mistrustful of a Christian which was not a Christian.

The birth of Frederick II

Even his birth was remarkable. According to chronicles from the era, in order to stanch any doubt about his origin, the already 40-year old Constance gave birth to the child publicly in a marketplace. After Henry VI, his father, died at 31, Frederick came under the guardianship of the pope, which the latter, however, neglected him on the basis of power-politics. In Palermo, where the three-year-old boy was brought after his mother's death, he grew up like a street youth. On his own, he roamed a city which swarmed with adventurers and pirates, beggars and jugglers, Arab and Jewish merchants. The only benefit from Innocent III was that at 14 years of age he married a 25-year-old widow named Constance, the daughter of the king of Aragon in what is now Spain. As it happened, both seemed reasonably happy with the arrangement, and Constance soon bore a son, Henry.

Later, it appeared opportune to Innocent III to support Frederick as a legitimate king, in order to counter the Emperor Otto � whom up to that time the pope had supported. In 1212 he brought him to Rome, gave him a round of instruction in things political, and sent him, provided with a bull of excommunication against the Guelph Otto, in the direction of Germany. The voyage seemed difficult, as the sea was roamed by the ships of Pisa, as usual faithful to the official emperor, and the road north to Rome were commanded by imperial garrisons. But in that period of his life a kind of mystic and prophetical luck seemed to illuminate every step made by the young king.

Frederick managed to reach Liguria with ships sent by the fiercest rival of Pisa, Genova, where he stayed for three months. He crossed the Alps using the most difficult passes, as the Brenner Pass was occupied by the enemy troops of the duchies of Merano and Bavaria, and then he came to Konstanz in territory of the archbishop of Chur. The city was in fact preparing to receive the emperor, and would not allow the new aspirant to the imperial title to remain in the city. However, after a solemn reading of the pope's Bull of Excommunication, the gates of the city were opened for him. Otto, who meanwhile had waited in �berlingen for the ferry, came three weeks later before the city gates and was turned away. Frederick conquered the realm by means of generous promises and donations, without spilling a drop of blood. Otto, crushed in the Battle of Bouvines by the French, died some years later, a lonely man in the Harzburg, while Frederick would be crowned Emperor in Rome by the pope. In his coronation, too, he showed how unusual he was. At his coronation he carried a brand-new, red coronation robe with a strange ornamentation at the edge. In reality it was an Arabic inscription, which indicated that this robe dated from the year 528, not by the Christian but by Muslim calendar! About this was an Arab benediction: "May the Emperor be received well, may he enjoy vast prosperity, great generosity and high splendor, fame and magnificent endowments, and the fulfillment of his wishes and hopes. May his days and nights go in pleasure without end or change". This coronation robe can be found today in the Schatzkammer of the Kunsthistorisches Museum in Vienna.

This was typical of him: while he was being crowned by the Pope to be the highest defender of the Christian faith, his coat referred to the history of Islam. And not only that. He did not exterminate the Saracens of Sicily with fire and sword; on the contrary, he allowed them to settle on the mainland and even to build mosques. Not least, he enlisted them in his - Christian - army and even into his personal bodyguards. As these were Muslim soldiers, they were immune from papal excommunication. These among others are reasons that Frederick II is listed as a representative member of the sixth region of Dante's Inferno, The Heretics who are burned in tombs.

A further example of how much he differed from his contemporaries was his Crusade in the Holy Land. Outside Jerusalem, with the power to take it, he parlayed five months with the Egyptian Sultan al-Kamil about the surrender of the city. The Sultan summoned him into Jerusalem and entertained him in the most lavish fashion. When the muezzin, out of consideration for Frederick, failed to make the morning call to prayer, the emperor declared: "I stayed overnight in Jerusalem, in order to overhear the prayer call of the Muslims and their worthy God". The Saracens had a good opinion of him, so it was no surprise that after five months Jerusalem was handed over to him, taking advantage of the war difficulties of al-Kamil. The fact that this was regarded in the Arab as in the Christian world as high treason did not matter to him one whit. As the Patriarch of Jerusalem refused to crown him king, he set the crown on his own head.

Besides his great tolerance (which, however, did not apply to Christian heretics), he had an unlimited thirst for knowledge and learning. To the horror of his contemporaries, he simply did not believe things that could not be explained by reason. So he forbade trials by ordeal on the firm conviction that in a duel the stronger would always win, whether he was guilty or not. Also, it can be forgotten amidst the general enthusiasm over his book on falconry releases frequently that he also wrote a scientific book about birds or that many of his laws continue to affect life down to the present day, such as the prohibition on physicians acting as their own pharmacists. This was a blow at the charlatanism under which physicians diagnosed dubious maladies and also at the same time in order to sell a useless, even dangerous "cure".

Frederick's greatest passion were animals, and falcons in particular. He inherited his love for falconry from his Norman ancestors. According to a source, Frederick replied to a letter in which the Mongol khan invited him to submit that he was keen to do it, provided he was permitted to become the khan's hawker. He mantained up to 50 hawkers a time for his court, and in his letters he requested the acquiring of Arctic gerfalcons from L�beck and even from Greenland. He commissioned the translation of the treaty De arte venandi cum avibus, by the Arab Moamyn, to his Syrian astrologer Theodor, but he corrected or rewrote it during the endless siege of Faenza. This implies that the Emperor knew the Arab language very well. Frederick picked up information from many of the philosphers then known, and mainly from the De Animalibus by Aristotle, creating a really noteworthy scientific work for the time it was written. One of the two existing versions was modified by his son Manfred, also a keen adherent of falconry. Frederick loved exotic animals in general: his mobile zoo, with which he used to impress the cold cities of Northern Italy and Europe, included hounds, elephants, giraffes, cheetahs, lynxs, leopards and exotic birds. In 1232 he sent the Egyptian sultan a rare white bear, in exchange for a planetary worth 20,000 marks: Frederick was in fact attracted by stars, and his court was full of astrologers and astronomers. He often issued letters to the main scholars of the time (not only in Europe) asking for solutions to questions of science, mathematics and physics.

A Damascene chronicler, Sibt ibn al-Jawzi, leaves a physical description of Frederick based on the testimony of those who had seen the emperor in person in Jerusalem. "The Emperor was covered with red hair, was bald and myopic. Had he been a slave, he would not have fetched 200 dirhams at market." His eyes were described variously as blue, or "green like those of a serpent".

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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 (St�rner) 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.

I'm a bit surprised no one has mentioned Henry V of England.  Sure, a lot of his "greatness" comes from being immortalized by Shakespeare but I really think he deserves a place near the top of the rankings.

Before even coming to the throne, he proved his military capabilities fighting first against Hotspur and later Owain Glyndwr and the Welsh.  By the time he was king, he faced an unhappy, divided England.  By pardoning the heirs of the men who had fought with his father, Henry gradually gained loyalty, ending the quasi-anarchy that had characterized his father's reign, and creating a new spirit of nationalism.  He was also extremely considerate of his poorer subjects, making him a hero with the populace.  

Of course, Henry's main challenge was to reestablish England's position as one of great countries of Europe.  This he did by claiming France as his.  Once again, he showed his military brilliance, defeating the much larger French forces and succeeding in doing what generations of monarchs had failed at: the unification of the French and English crowns.

Henry also gets credit for helping end the Great Schism by securing the election of Pope Martin V.  This obviously put England back on the map and gave Henry a prominent position in Christendom, which allowed him to make plans for a Crusade. 

Perhaps he died too young for us to really tell if he belongs among the greats.  But I think he at least deserves a mention.

Originally posted by Frederick Roger Guess all that Carolingian Renaissance thing is just a load of bollocks, then...

Yes and no, depends on what you expect of this renaissance. Compared with the Italian renaissance of the late middle ages, the Carolingian one was nothing more than a passing fling with the fine culture of Antiquity, by the semi-civilized, Frankish warrior aristocracy.

Describing Charlemagne as a "barbarian butcher" is wee bit too harsh for my tastes. Of course he was a warrior, the only ones who can't be described as butchers at this point are the monks. Charlemagne did attempt to gain some mastery of letters, but as he began his education as such a late age as he did, he never advanced much. A civilizing influence nonetheless, quite outstanding for his time.

Even though I already vouched for Emperor Frederick II Hohenstaufen as greatest medieval potentate, Charlemagne is IMO also a good candidate, others could be Otto I (the great), Philip II August of France, Roger II of the Two Sicilies, or Baldwin I of Jerusalem (a cunning bastard).

In all my opinion for the best is;

THE WORLD- Chinggis khaan

EUROPE- Charlemagne

Hmmmm... my vote goes to William of Normandy, if the impact of his conquest of England during the 1000s is the base, He made a great foundation to make England one of the mighty countries until now...

Flemish Keizer Karel V?