Charles V (Spanish: Carlos I; Dutch: Karel V; German: Karl V.; Italian: Carlo V; Czech: Karel V.; French: Charles Quint; 24 February 1500 – 21 September 1558) was ruler of the Holy Roman Empire from 1519 and, as Charles I, of the Spanish Empire from 1516 until his voluntary retirement and abdication in favor of his younger brother Ferdinand I as Holy Roman Emperor and his son Philip II as King of Spain in 1556.
Charles was the eldest son of Philip the Handsome and Joanna the Mad. His grandmother was Isabella I of Castile. As the heir of three of Europe's leading dynasties—the House of Habsburg of the Habsburg Monarchy; the House of Valois-Burgundy of the Burgundian Netherlands; and the House of Trastámara of the Crowns of Castile and Aragon—he ruled over extensive domains in Central, Western, and Southern Europe; and the Spanish colonies in the Americas and Asia. As Charles was the first king to rule Castile, León, and Aragon simultaneously in his own right, he became the first King of Spain. In 1519, Charles became Holy Roman Emperor and Archduke of Austria. From that point forward, his empire spanned nearly four million square kilometers across Europe, the Far East, and the Americas.
These lineages were eventually united by the marriage of the Catholic Monarchs, Ferdinand II of Aragon (king of the Crown of Aragon) and Isabella I of Castile (queen of the Crown of Castile). Although their kingdoms continued to be separate, with their personal union they ruled them together as one dominion. Ferdinand also conquered the southern part of Navarre and annexed it to what was to become Spain. Isabella left her kingdom to her daughter Joanna of Castile. Ferdinand served as her regent during her insanity; though rebuffed by the Castilian nobility and replaced by Joanna's husband Philip the Handsome, he resumed his regency after Philip's death. In 1516, after Ferdinand II's death, his daughter Joanna inherited the kingdom of Aragon, but was kept prisoner at Tordesillas as insane. As Joanna's son, the future Holy Roman Emperor Charles V, did not want to be merely a regent, he was proclaimed king of Castile and Aragon jointly with his mother in Brussels. Subsequently, Castilian and Aragonese Cortes alleged oath to him as co-king with his mother. Upon her death, he became sole King of Castile and Aragon, and the thrones were thereafter united permanently.