Frederick Ii, Holy Roman Emperor Puns

Hey there! I just want to preface this by saying I checked the book recommendations on this reddit and couldn't find one quite matching what I'm looking.
Essentially, I am looking for a present for a tutor who was at my school for over 30 years, transformed the lives of dozens of people, and has been forced to retire due to the COVID 19 pandemic. He was an expert in languages, graduating from Oxford, and erudite on German history. Essentially, the book can be in English, French or German and ought to be more than a balanced general book and more of an academic text.

He had a niche interest in Medieval German history, in particular Holy Roman Emperor Frederick II. Do any historians here who are proficient in Holy Roman Imperial history have any recommended books on this person? I ask here as, since he is an academic, he would likely benefit most from an academic's recommendation. I'm a theologian so other than Church histories not sure where would be best to start for a proper text on this person.

I have a habit of playing Crusader Kings 2 and listening to fittingly appropriate real medieval music that I find on YouTube and such when playing the game. Through following down the YouTube recommendations rabbit hole, I came across a song called D'un sirventes far. You can listen to it here. From looking it up, I discovered that the artist, Guilhem Figueira, was an Occitanian troubadour of Cathar background, who was exiled and who made his way to the court of Frederick II, and that the lyrics were harshly anti-papal. Wondering how he made it there unscathed, I soon found out that the Emperor was completely detested by the Roman Papacy, which made sense as to why a fellow like Figueira found himself there with comfort.

But this made me wonder, and especially so considering the era and how we often think of it... how on earth did Frederick II maintain his reign as king? How would his subjects accept his reign, given the unquestionable and unmatchable power and influence of the Papacy? Additionally, were there other occurrences like this throughout medieval Christendom? Are our perceptions of the all-powerful and unquestionable Papacy of medieval Europe incorrect? And of course, what was Frederick II's beef with the Pope, and how did it all start?

Would they have been all European women? Arabs? Would there have been any Muslim women? Were there men as well? Do we know what his subjects thought of this?

A novel about the life of this great statesman and culture lover

Frederick II (1194-1250) was the son of the Emperor Heny VI and the Norman queen of sicily Constance. So he was at the same time King of Sicily and Emperor of Germany. Born in central Italy, he had German, Sicilian, Viking and French blood.

He considered himself the successor of Roman Emperors of antiquity, but in reality acted as a proto-modern monarch establishing the first state university and abolishing the trial by ordeal. Deeply catholic, he was nonetheless influenced by the Muslims of sicily and entered in philosophical debates with the Islamic scholars of the Mediterranean. Fibonacci, the mathematician that brought Arab numerals to Europe, was at his court.

Since the HRE included northern italy and Sicily controlled southern Italy, the Popes reluctanctly agreed to have the Papal states encircled by his dominions. In exchange, they obtained the promise by Frederick to organize a crusade to recapture the Holy Land. And yet Frederick was hostile to enter a religious war with the muslims, so he obtained the crowns of Jerusalem, Nazareth and Betlehem, via marriage and diplomacy rather than conflict.

At the peak of his power he controlled much of central Europe and almost all of Italy. Subutai and the Khan asked him in an embassy to sumbit all of his territories to the Mongols and he refused.

Called the "Anti-christ" by his enemies and the "Wonder of the World" by his supporters, he was excommunicated three times and de-excommunicated twice.

Frederick was viewed as an Italian King by the German princes and as German Emperor by Italian republicans. He lost his power in the context of civil wars and rebellions with the cities of the Empire. His territories were divided by his heirs and enemies.

As part of the Third Crusade, Emperor Frederick Barbarossa arrived at Constantinople with a significantly large army in 1185. At the time, the city was under the rule of Byzantine Emperor Isaac II Angelos (who would have only recently assumed power).

As far as I can tell, this is the first (and only?) time a reigning Holy Roman Emperor visited the city during Byzantine times (Barbarossa had been there once before in a previous crusade, but that's before he was crowned emperor).

With the two empires constantly competing over which was the legitimate Roman Empire, did anything interesting transpire between the two emperors Barbarossa and Isaac? Do we know anything about any potential meetings? Had Byzantine-Holy Roman relations changed significantly since the days of Charlemagne at this point or was there still a mutual distaste over the use of the imperial title?

Called the "first European," by Nietzsche and considered the first modern ruler by many historians.

https://en.wikipedia.org/wiki/Frederick_II,_Holy_Roman_Emperor