Charles V 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.
Much of Charles' reign was devoted to the Italian Wars against France which, although enormously expensive, were militarily successful. Charles' forces re-captured both Milan and Franche-Comté from France after the decisive Habsburg victory at the Battle of Pavia in 1525, which pushed Francis to form the Franco-Ottoman alliance. Charles' rival Suleiman the Magnificent conquered the central part of the Hungarian Kingdom in 1526 after defeating the Christians at the Battle of Mohács. However, the Ottoman advance was halted after they failed to capture Vienna in 1529.