Cuban Defense Minister Raul Castro is President Fidel Castro's staunchly loyal younger brother and his designated successor. At 75 and five years younger than Fidel, Raul is far less charismatic than his brother though far more radical.

Monday night, Fidel temporarily relinquished his presidential powers to Raul, telling Cubans in a letter read on television that he underwent surgery. The Cuban leader said he had suffered gastrointestinal bleeding, apparently due to stress from recent public appearances in Argentina and Cuba.

As first vice president of the Council of State, Cuba's supreme governing body, Raul is legally designated to assume his brother's role as president of the council in the event of "absence, illness or death."

Related story: Timeline: Cuba Under Castro

Three weeks after taking power in January 1959, Castro named Raul his successor, telling supporters: "Behind me are others more radical than I."

He officially designated Raul as his successor at a Communist Party congress in October 1997, saying "Raul is younger than I, more energetic than I. He can count on much more time."

As head of Cuba's armed forces, Raul has been deeply involved in Cuba's military involvement in Angola and Ethiopia during the 1970s — as well as with the military's successful peacetime efforts to help rescue Cuba's economy following the collapse of the Soviet Union in 1991.

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Although usually working behind the scenes, Raul briefly assumed a higher profile during the seven-month fight to return Cuban boy Elian Gonzalez to his homeland from Florida in 2000.

While Fidel headed up many of the mass protests in Havana, it was the mustachioed Raul, dressed in his olive green uniform and a full head shorter than his brother, leading tens of thousands of chanting, flag-waving citizens in the provinces.

In one rare interview in early 2001, Raul spoke with unusual frankness about his older brother's eventual death and encouraged the United States to make peace with Cuba while Fidel was still alive.

"I am among those who believe that it would be in imperialism's interest to try, with our irreconcilable differences, to normalize relations as much as possible during Fidel's life," Raul said in the interview with state television. Later, he said, "it will be more difficult," implying he would be harder to deal with.

Raul, a political hardliner, belonged to a Communist youth group even before the revolution. The elder Castro didn't publicly embrace socialism until 1961.

But on the economic front, he showed signs of flexibility.

As defense minister, Raul has overseen some of Cuba's most important experiments with limited market-style reforms. Military units produced and sold food at free markets and the military ran an important tourism company, Gaviota.

He also expressed interest in China's version of free-enterprise socialism during a November 1997 visit.

In 1962 he became deputy prime minister and in 1972 first deputy prime minister, behind Fidel.

Like his brother, Raul has been suspicious of the United States and at a September 1960 rally denounced the U.S. Embassy as "a cave of spies."

In a July 1962 visit to the Soviet Union, Raul was given a promise of Soviet missiles — a development that led to the U.S.-Soviet missile crisis of October 1962 which brought the world to the brink of nuclear war.

Yet Raul made occasional conciliatory moves toward the United States. In 1964, he said he was willing to hold talks with the Americans "even on the moon."