Profile: Raul Castro
Raul Castro has played a central role in Cuba's recent history
Raul Castro, for nearly half a century Cuba's second-in-command, has in fact been its stand-in leader for the past 18 months.
He looks set to continue in the role for a few more days at least - and may have his eye on official promotion to the post - after his older brother, the long-time Cuban leader Fidel Castro, announced he was stepping down.
Cuba's National Assembly will elect a new president on 24 February. Raul is likely to be one of the leading candidates.
Raul, now 76, has always lurked in his brother's shadow - a head shorter than Fidel, and without his brother's charisma or oratorical verve.
As head of Cuba's armed forces, Raul has played a central role in Cuba's recent history, and yet opinion is divided over the role he might play as Cuban leader.
Raul was officially designated Fidel's successor at a Communist Party congress in October 1997, when Fidel said: "Raul is younger than I, more energetic than I. He can count on much more time."
Behind me are others more radical than I
Fidel Castro in 1997
But the two have worked together since the 1950s, when they plotted the Cuban Revolution.
Raul can claim an earlier commitment to socialism than his brother, whose early defining political characteristic was nationalism.
Some say that he has always been more of a hard-liner than Fidel. In the first few months of the Revolution, he was kept out of the limelight because his militancy was thought unpalatable.
But analysts are divided about how radical a leader he might make now.
Raul was born in 1931 in the eastern province of Holguin, to Angel Castro and Lina Ruz, the youngest of three brothers - five years younger than Fidel.
Castro's father was a wealthy sugar planter
He attended school first in Santiago and then in Havana, where as a university undergraduate he joined a communist youth group.
In 1953, he took part with Fidel in the assault on the Moncada barracks - an attempt to oust the authoritarian regime of Fulgencio Batista.
But the assault failed, and Raul served 22 months in jail alongside his brother. In 1955, the two were released, and went to Mexico to prepare the ship Granma for a revolutionary expedition to Cuba in late 1956.
During this time, Raul is said to have befriended Che Guevara, introducing him to Fidel.
Upon their arrival back in Cuba, the band of revolutionaries conducted a guerrilla warfare campaign from the Sierra Maestra mountains, finally overthrowing Batista in early 1959.
That early guerrilla army has evolved under Raul's leadership into a fighting force of some 50,000, which assisted pro-Soviet forces in conflicts in Angola and Ethiopia during the 1970s.
Raul has for decades been Fidel's right-hand man
The army played a crucial role in peacetime efforts to prop up the ailing Cuban economy following the collapse of the Soviet Union in 1991. Through a state-run tourism company, Gaviota, it also plays a primary role in the - now key - sector of tourism.
Raul is also reported to have influenced financial policy from behind the scenes.
As well as being defence minister and first vice-president of the Council of State - the constitutional successor to Fidel - Raul Castro is vice-secretary of the Politburo and the Central Committee of the Communist Party of Cuba.
But Raul indicated in June 2007 that a collective leadership would most likely govern Cuba following his brother's death, through the Communist Party, which is reportedly being strengthened in preparation for such a succession.
Analysts are divided on what kind of leader he might make. They suspect that as long as Fidel is alive he will have a strong influence on government.
It has been suggested that Raul would make a more radical leader than his brother. Fidel said in 1997: "Behind me are others more radical than I."
But others suggest he would help the country make the transition to a "softer", more market-friendly form of communism.
He has raised expectations of economic reforms in Cuba, saying that it required "structural changes", and acknowledging that many people could not get by on government-decreed wages.
But he has not made any such changes yet.
Spain, which has a policy of constructive engagement towards Cuba, responded to news of Fidel's retirement by urging Raul "to take on his reform project with a greater capacity, toughness and confidence".
In 1959 Raul married Vilma Espin, a fellow revolutionary guerrilla fighter and high-level party official, who died in June 2007.
The couple had four children. Raul is said to be a doting father and enthusiastic climber.