The Wikipedia article skips over the most important bit: in 1245 Pope Innocent IV declared that Emperor Frederick II was deposed.

So how do we get from there to Richard of Cornwall being a candidate for emperor? Well it’s pretty complicated, but it has to do with the relationship between the pope and the empire in general, between Frederick II and specific popes, as well as marriages between English royalty and Frederick and his family members.

First, for the papacy, the pope was the spiritual leader of Latin Christendom and was traditionally responsible for crowning the Holy Roman Emperor, since that’s what happened all the way back in the days of Charlemagne. I’m simplifying things a lot, but basically the German nobility elected a king of Germany and king of the Romans, and then the pope crowned him as emperor.

So did the pope have authority over the emperor, or did the emperor have authority over the pope? Starting in the 11th century, various popes introduced legal and administrative reforms that made the church a much more powerful, centralized authority, so they were able to emphasize the idea that the Holy Roman Empire was a secular arm of the church. By the early 13th century the popes were probably at the height of their power.

The Pope wasn’t just the spiritual leader of all Latin Christians though, he was also the monarch of his own kingdom, the Papal States in central Italy. Northern Italy was nominally part of the Holy Roman Empire but also contained various independent city-states that were sometimes allied with the Empire and sometimes rebelling against it. Meanwhile, southern Italy was part of the Kingdom of Sicily.

In 1194, the Emperor, Henry VI, married the queen of Sicily, Constance, and they had a son, Frederick. Henry died a few years later in 1197 and Constance died in 1198. The infant Frederick inherited Sicily from Constance, but the electors in Germany and Italy didn’t necessarily have to elect the previous emperor’s son. Should one person rule both Germany and Sicily? The Papal States would be surrounded, so the pope was not in favour of that, and the German nobles weren’t enthusiastic about electing a foreign child. There were other claimants, there was civil war and assassinations, and the dispute dragged on until Frederick was 18 in 1212, when he was finally elected king of Germany and of the Romans and crowned as emperor.

And now just as everyone had feared, Frederick was the emperor and the king of Sicily. The Papal States were surrounded by one monarch. His relationships with the popes (Innocent III, Honorius III, and Gregory IX) were not great, sometimes to the point that they were actually at war with each other. In 1227 Gregory IX excommunicated for him for not going on crusade at the agreed-upon time. Gregory also tried to depose him in 1240, but Frederick interrupted the council and imprisoned some of the bishops. Gregory died in 1241 and the next pope, Innocent IV, finally did manage to declare Frederick deposed at the Council of Lyon in 1245:

“The beast of blasphemy rises from the sea replete with names, which with the feet of a bear and the mouth of a lion, raging and formed in the rest of its limbs like a panther, opens its mouth in blasphemies against the divine name and does not omit to attack with similar darts His tabernacle and the saints who dwell in the heavens…look carefully at the head, middle and end of that beast Frederick, called emperor, and as far as you find abominations in the words of that man and wickedness, arm sound souls with the shield of truth against the treacheries of that man…” (Rist, The Papacy and Crusading in Europe, 1198-1245)

When the Pope thinks you’re the literal Antichrist there’s not much chance for reconciliation! Frederick held on for a few more years until he died in 1250, but after 1245 the pope and most other European kings considered both the empire and the Kingdom of Sicily vacant. They could all scheme to have their own candidates crowned instead.

The English had an interest in both crowns because they had long been connected to the Empire and to Sicily through marriage. In Sicily, Joan, the sister of Richard I and John of England, was married to a king William II (who was actually Constance’s nephew, although he ruled before her). Frederick II’s second wife was John’s daughter Isabella so the English were connected to the empire as well, although Isabella had died in childbirth in 1241. John’s other children, Isabella’s siblings, included the current king of England, Henry III, as well as Richard of Cornwall.

After Frederick was deposed in 1245, his whole family became ineligible to rule anywhere, according to the pope, at least. But Frederick continued to act as emperor until he died in 1250, and his son Conrad (from his first wife) then claimed both Sicily and the empire until he died too in 1254. Then Conrad’s son Conradin also continued the claim until 1268 (although he was just a child so other people defended the claim for him).

So Frederick’s family claimed to be the legitimate rulers on the one hand, but on the other the pope invited other people to rule Sicily and the empire. In 1252 Sicily was offered to Richard of Cornwall, but Richard thought this was preposterous. Supposedly he said it was “as if any one said to him, 'I give or sell you the moon, climb up and take it.'" Innocent also offered Sicily to Charles of Anjou, the brother of king Louis IX of France, who also rejected it at first. Henry III suggested his son, Edmund, who claimed to he king until 1263 although he never went there and was never king in any practical way. In 1263 Charles of Anjou decided he wanted it after all. Charles was the actual king of Sicily from 1268 (when he defeated and executed Conradin) until the Sicilian Vespers rebellion in 1282.

Richard thought it was much more reasonable to try to get elected as Holy Roman Emperor. “Brother of the emperor’s deceased wife” is a pretty weak claim though. There were other claims although they weren’t really any better. Pope Innocent IV initially gave his support to Heinrich Raspe, the Landgrave of Thuringia, although Raspe died in 1247. Count William II of Holland was then elected king of Germany by some of the electors, until he died in 1256. Some of the electors supported Richard, but some of them preferred king Alfonso X of Castile. Alfonso never came anywhere near Germany so it was easier for Richard to convince the electors to support him; he was also extraordinarily rich and was willing to pay/bribe anyone he needed to support him.

So he was elected king of Germany and king of the Romans, but he was never crowned emperor by the pope. He didn’t live in Germany and didn’t spend much time there, so his claim to the titles is kind of dubious, but after 1257 he is sometimes known as “Richard of Almain”, from the French name for Germany. He continued to use these titles until his death in 1273. Others were elected king of Germany after him, but no emperor was crowned until 1312, almost 70 years after Frederick II was deposed.

Sources:

Rebecca Rist, The Papacy and Crusading in Europe, 1198-1245 (Bloomsbury, 2011)

Alfred Haverkamp, Medieval Germany 1056-1273 (Oxford University Press, 1992)

David Abulafia, Frederick II: A Medieval Emperor (Oxford University Press, 1992)

Bjorn Weiler, Henry III and the Staufen Empire (Boydell, 2006)

David Carpenter, Henry III (Yale University Press, 2020)

Brett Edward Whalen, The Two Powers: The Papacy, the Empire, and Struggle for Sovereignty in the Thirteenth Century (University of Pennsylvania Press, 2019)

And some previous answers of mine for similar questions:

Why Edmund Crouchback had claim to Kingdom of Sicily?

Holy Roman Emperor Frederick II was excommunicated numerous times, fought several wars with the Papacy, and was called the Antichrist by Pope Gregory IX. This was all during the 13th century, a time we often think of as incredibly devout to Roman Christian authority. Just how did he keep his reign?

Could a Holy Roman Emperor be removed?