Juan Carlos I (/ˌhwɑːŋˈkɑːrloʊs/, Spanish: [xwaŋˈkaɾlos]; Juan Carlos Alfonso Víctor María de Borbón y Borbón-Dos Sicilias, born 5 January 1938) reigned as King of Spain from 1975 to 2014, when he abdicated in favour of his son, Felipe VI.

Juan Carlos is the grandson of Alfonso XIII, the last king of Spain prior to the monarchy's abolition in 1931 and the subsequent declaration of the Second Spanish Republic. Juan Carlos was born in Rome, Italy during his family's exile. Following his victory in the Spanish Civil War in 1939, Generalísimo Francisco Franco, the Spanish dictator, took over the government of Spain and in 1947, abolished the republican form of government and declared Spain to be a monarchy. Franco declared himself to be "Regent" while no monarch was designated. Juan Carlos's father, Don Juan, was the fourth child of Alfonso who had renounced his claims to the throne in January 1941. Don Juan was seen as too liberal for Franco and in 1969, bypassed his father and selected Juan Carlos as his successor and the next head of state, expecting him to continue the authoritarian regime.

Juan Carlos spent his early years in Italy and came to Spain in 1947 to continue his studies. After completing his secondary education in 1955, he began his military training and entered the General Military Academy at Zaragoza. Later, he attended the Naval Military School, the General Academy of the Air, and finished his tertiary education at the University of Madrid. In 1962, Juan Carlos married Princess Sophia of Greece in Athens, daughter of King Paul. The couple had two daughters and a son together: Elena, Cristina, and Felipe. Due to Franco's declining health, Juan Carlos first began acting as Spain's head of state in the summer of 1974. Franco died in November the following year and Juan Carlos became king on 22 November 1975, two days after Franco's death, the first reigning monarch since 1931; although his exiled father did not formally renounce his claims to the throne in favor of his son until 1977.

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