Charles V (Spanish: Carlos; German: Karl; Italian: Carlo; Dutch: Karel; Latin: Carolus; 24 February 1500 – 21 September 1558) was ruler of both the Holy Roman Empire from 1519 and the Spanish Empire (as Charles I of Spain) from 1516, as well as of the lands of the former Duchy of Burgundy from 1506. He stepped down from these and other positions by a series of abdications between 1554 and 1556. Through inheritance, he brought together under his rule extensive territories in western, central, and southern Europe, and the Spanish viceroyalties in the Americas and Asia. As a result, his domains spanned nearly 4 million square kilometres (1.5 million square miles), and were the first to be described as "the empire on which the sun never sets".

Charles was the heir of three of Europe's leading dynasties: Valois of Burgundy, Habsburg of Austria, and Trastámara of Spain. As heir of the House of Burgundy, he inherited areas in the Netherlands and around the eastern border of France. As a Habsburg, he inherited Austria and other lands in central Europe, and was also elected to succeed his grandfather, Maximilian I, as Holy Roman Emperor. As a maternal grandson of the Catholic Monarchs of Spain, from the Spanish House of Trastámara he inherited the Crown of Castile, which was developing a nascent empire in the Americas and Asia, and the Crown of Aragon, which included a Mediterranean empire extending to southern Italy. Charles was the first king to rule Castile and Aragon simultaneously in his own right (as a unified Spain), and as a result he is often referred to as the first king of Spain. The personal union under Charles of the Holy Roman Empire with the Spanish Empire was the closest Europe would come to a universal monarchy since the time of Charlemagne in the 9th century.