Charles X Gustav, also Carl Gustav (Swedish: Karl X Gustav; 8 November 1622 13 February 1660), was King of Sweden from 1654 until his death. He was the son of John Casimir, Count Palatine of Zweibrcken-Kleeburg and Catherine of Sweden. After his father's death he also succeeded him as Pfalzgraf. He was married to Hedwig Eleonora of Holstein-Gottorp, who bore his son and successor, Charles XI. Charles X Gustav was the second Wittelsbach king of Sweden after the childless king Christopher of Bavaria (14411448) and he was the first king of the Swedish Caroline era, which had its peak during the end of the reign of his son, Charles XI. He led Sweden during the Second Northern War, enlarging the Swedish Empire. By his predecessor Christina, he was considered de facto Duke of Eyland (land) before ascending to the Swedish throne.

His numbering as Charles X derives from a 16th-century invention. The Swedish king Charles IX (16041611) chose his numeral after studying a fictitious history of Sweden. This king was the fourth actual King Charles, but has never been called Charles IV.

Christina (Swedish: Kristina, Swedish pronunciation: [krɪ²stiːna]; 18 December 1626 – 19 April 1689), a member of the House of Vasa, was Queen of Sweden from 1632 until her abdication in 1654. She succeeded her father Gustavus Adolphus upon his death at the Battle of Lützen in 1632, but began ruling the Swedish Empire when she reached the age of eighteen in 1644.The Swedish queen is remembered as one of the most learned women of the 17th century. She was fond of books, manuscripts, paintings, and sculptures. With her interest in religion, philosophy, mathematics, and alchemy, she attracted many scientists to Stockholm, wanting the city to become the "Athens of the North". The Peace of Westphalia allowed her to establish an academy or university when and wherever she wanted.In 1644, she began issuing copper in lumps as large as fifteen kilograms to serve as currency. Christina's financial extravagance brought the state to the verge of bankruptcy, and the financial difficulties caused public unrest. Christina argued for peace to end the Thirty Years' War and received indemnity. Meanwhile, she caused a scandal when she decided not to marry, and when she converted to Catholicism secretly in Brussels and publicly in Innsbruck. The "Minerva of the North" relinquished the throne to her cousin, and settled in Rome.Pope Alexander VII described Christina as "a queen without a realm, a Christian without faith, and a woman without shame." Notwithstanding, she played a leading part in the theatrical and musical community and protected many Baroque artists, composers, and musicians.

Being the guest of five consecutive popes, and a symbol of the Counter Reformation, Christina is one of the few women buried in the Vatican grotto. Her unconventional lifestyle and masculine dressing have been featured in countless novels, plays, operas, and film. In all the biographies about Christina, her gender and cultural identity play an important role.