Queen of Aragon in the context of Catalan Constitutions

Joanna of Castile (6 November 1479 – 12 April 1555), historically known as Joanna the Mad (Spanish: Juana la Loca), was the nominal queen of Castile from 1504 and queen of Aragon from 1516 to her death in 1555. She was the daughter of Queen Isabella I of Castile and King Ferdinand II of Aragon. Joanna was married by arrangement to the Austrian archduke Philip the Handsome on 20 October 1496. Following the deaths of her elder brother John, elder sister Isabella, and nephew Miguel between 1497 and 1500, Joanna became the heir presumptive to the crowns of Castile and Aragon. When her mother died in 1504, she became queen of Castile. Her father proclaimed himself governor and administrator of Castile.

In 1506, Joanna's husband Philip became king of Castile jure uxoris as Philip I, initiating the rule of the Habsburgs in the Spanish kingdoms. Philip died that same year. Despite being the ruling queen of Castile, Joanna had little effect on national policy during her reign as she was declared insane and confined in the Royal Palace in Tordesillas under the orders of her father, who ruled as regent until his death in 1516, when she inherited his kingdom as well. Her son Charles I became king, and during his reign Joanna was nominally co-monarch but remained confined until her death. Joanna died aged 75 in 1555, at which point her son Charles, the Holy Roman Emperor, became the sole ruler of Castile and Aragon.

Isabella I (Spanish: Isabel I; 22 April 1451 – 26 November 1504), also called Isabella the Catholic (Spanish: Isabel la Católica), was Queen of Castile and León from 1474 until her death in 1504. She was also Queen of Aragon from 1479 until her death as the wife of King Ferdinand II. Reigning together over a dynastically unified Spain, Isabella and Ferdinand are known as the Catholic Monarchs. Her reign marked the end of Reconquista and also the start of Spanish Empire and dominance of Spain over European politics for the next century.

Isabella's marriage to Ferdinand of Aragon in 1469 created the basis of the de facto unification of Spain. With Ferdinand's help, she won the War of the Castilian Succession, securing her position as Queen of Castille. Isabella reorganized the governmental system, brought the crime rate down, and unburdened the kingdom of the debt which her half-brother King Henry IV had left behind. Her reforms and those she made with her husband had an influence that extended well beyond the borders of their united kingdoms.

Petronilla (29 June/11 August 1136 – 15 October 1173), whose name is also spelled Petronila or Petronella (Aragonese: Peyronela or Payronella, and Catalan: Peronella), was Queen of Aragon (1137–1164) from the abdication of her father, Ramiro II, in 1137 until her own abdication in 1164. After her abdication she acted as regent during the minority of her son Alfonso II of Aragon (1164–1173). She was the last ruling member of the Jiménez dynasty in the Kingdom of Aragon, and by marriage to Ramon Berenguer IV, Count of Barcelona brought the House of Barcelona to the throne of Aragon, uniting the Kingdom of Aragon with the County of Barcelona to create the Crown of Aragon.