Frederick I was King of Sweden from 1720 until his death, having been prince consort of Sweden from 1718 to 1720, and was also Landgrave of Hesse-Kassel from 1730. He ascended the throne following the death of his brother-in-law absolutist Charles XII in the Great Northern War, and the abdication of his wife, Charles's sister and successor Ulrika Eleonora, after she had to relinquish most powers to the Riksdag of the Estates and thus chose to abdicate. His powerless reign and lack of legitimate heirs of his own saw his family's elimination from the line of succession after the parliamentary government dominated by pro-revanchist Hat Party politicians ventured into a war with Russia, which ended in defeat and the Russian tsarina Elizabeth getting Adolf Frederick of Holstein-Gottorp instated following the death of the king. Whilst being the only Swedish monarch called Frederick, he was Frederick I of Hesse-Kassel and thus Frederick I also of Sweden, though other Swedish monarchs with non-repeating names had not been enumerated.

A prince consort is the husband of a monarch who is not a monarch in his own right. In recognition of his status, a prince consort may be given a formal title, such as prince. Most monarchies do not allow the husband of a queen regnant to be titled as a king because it is perceived as a higher title than queen, however, some monarchies use the title of king consort for the role.