BOGOTA, Colombia — Raul Castro has lived in the shadow of his brother for all of his 75 years, but few Cubans doubt the capacity of the man who has been one of the pillars of the regime.

Any exiles harboring hopes that the regime will crumble when Fidel Castro’s rule ends may be bitterly disappointed. Raul Castro has shared his brother’s revolutionary fervor from the start.While he is believed to be open to the sorts of economic reforms that have transformed China, his commitment to communism is beyond doubt.

“Only the Communist Party, as the institution that brings together the revolutionary vanguard and will always guarantee the unity of Cubans, can be the worthy heir of the trust deposited by the people in their leader,” he said in June.

The man who trained the Castro brothers’ rebel force in Mexico, Alberto Bayo, said: “We have in Raul a colossus in the defense of revolutionary principles. Raul is Fidel multiplied by two in energy, in inflexibility, in fiber. Raul is tempered steel.”

Raul Castro has always been at his brother’s side. He was there on July 26, 1953, at the failed assault on the Moncada barracks that landed the brothers in the prisons of the dictator at the time, Fulgencio Batista.

It was not Fidel Castro but Raul Castro who first befriended the Argentine doctor Ernesto Guevara and brought the man who would become the worldwide symbol of the revolution into the Cuban revolutionary camp.

Raul Castro played a key role in the uprising that toppled Batista in 1959. Contemporaries saw him as even more ruthless than Fidel Castro and accused of executing more than 100 officers and soldiers of the Batista regime.

His role since has been as the second most powerful figure in the regime. His wife, Vilma Espin, plays the role of Cuba’s first lady, as Fidel Castro has no wife.

But at his advanced age, Raul Castro does not represent the long-term future of Cuba. He is reported to have been treated for prostate cancer and liver disease.