Spain's ex-PM Adolfo Suarez, who guided the nation through the turbulent years following the death of fascist dictator Francisco Franco, has died at 81.
Mr Suarez was taken to hospital on Monday suffering from a respiratory infection.
King Juan Carlos turned to him upon Franco's death in 1975 to try to unite Spain's disparate political factions.
Mr Suarez served as prime minister until 1981 and became one of the country's most respected politicians.
He had been suffering from Alzheimer's disease for about a decade, and died on Sunday afternoon at Madrid's Centro Clinic hospital.
King Juan Carlos has paid tribute, calling Mr Suarez an exceptional colleague and a true friend.
In a televised message, the king said Mr Suarez had been "guided at every turn by his loyalty to the crown and all that it represents, the defence of democracy, the rule of law, unity and the diversity of Spain".
'They changed history'
Mr Suarez's son, Adolfo Suarez Illana, praised both his father's and the king's role in the post-Franco period.
He said: "Thanks to the king, he was head of government. Thanks to the king, he was able to do what he liked at a unique moment in the history of Spain. Together, they changed the course of history."
Mr Suarez was a relatively unknown Francoist official in 1975, and faced criticism by both the left and right following his appointment by the king.
But in 1977 Mr Suarez contested and won Spain's first democratic elections since World War Two.
He moved to legalise political parties, including the communists, and oversaw the formation of a constitution that was adopted in 1978.
He was also noted as a calming voice during the tense period surrounding the attempted coup by Francoists on 23 February 1981.
Former PM Jose Luis Rodriguez Zapatero told Reuters: "Prime Minister Suarez's political career calls to mind the highest spirit of our democratic transition: recognition of dissenting voices, promotion of tolerance and the practice of dialogue.
"Thanks to that attitude he had the capacity to forge great agreements."