It is an opinion shared by many who are familiar with the 75-year-old's role in Cuban politics since the Fidelistas' overthrow of General Fulgencio Batista.

Within weeks of the Castro brothers seizing control, Raul was personally overseeing the executions of more than 100 soldiers and policemen loyal to the old regime. And, in his near half-century at the helm of Cuba's armed forces since, he has never hesitated to order the death or imprisonment of anyone he considered at odds with his view of the revolution, or anyone perceived as a personal threat. Memories are still fresh of the 1989 execution of General Arnaldo Ochoa, a popular Cuban war hero put to death with three others on Raul's orders after their conviction on trumped-up drugs charges.

Raul might be only five years younger than his brother, whose 80th birthday celebrations will go ahead today without the recovering charismatic leader, but there is nothing of the lovable, affable grandfather in him, an image Fidel loves to present to the world. Instead, he prefers the exclusive company of his inner circle, his wife Vilma Espin Guillois, another veteran of the revolution, and, if reports are to be believed, a regular bottle of rum.

'Raul isn't someone we should take lightly,' said Joe Garcia, former executive director of the Cuban American National Foundation, largest of the anti-Castro exile groups in the US. 'He's always played the bad cop in the good-cop, bad-cop game. But he's not Fidel in terms of assuming that role as charismatic international statesman. He's more of a local sovereign than cult personality.'

Nicknamed, though never to his face, La China because of looks (he is reputed to be the bastard son of a Chinese father), Raul's position of power comes from his iron grip on the military.

But his belligerent side was visible long before la revolucion, when he turned to communism years ahead of his brother.

He was a student activist and a member of Cuba's Socialist Youth movement, and during his time as a social sciences student at Havana's Belen College he enjoyed swimming, fishing and racing cars.

He was also an excellent marksman and was a key player in the first shots of the Cuban revolution, the ill-fated attack on the Moncada barracks in 1953, when the Castros' guerilla force was routed and after which he spent several years in exile in Mexico. It was there he introduced the Argentine revolutionary Che Guevara to Fidel, and the seeds of the modern day Cuba Communist Party were sown.

There is no sign of Raul mellowing with age, according to experts, despite economic and agricultural reforms he has overseen since the collapse of Cuba's major sponsor, the Soviet Union, in 1991.

'Should Raul permanently replace his ailing brother, the economy might benefit. Fidel is a dyed-in-the-wool believer in the central control once practiced by the Soviet Union. In contrast, Raul has praised the gradual economic liberalisation in China,' said George W. Grayson, professor of government at College of William and Mary in Williamsburg, Virginia.

But the professor warns that does not mean political change is on the way. 'Raul can ensure political stability because of his command of Cuba's large military and paramilitary forces,' he said.

So far, Raul has remained firmly out of sight since his brother's illness was announced, raising speculation in some quarters that he is working fervently behind the scenes to shore up his position of power among army generals. He is known to have run-ins with several high-ranking military officers, including Ramiro Valdes, Ramon Espinosa and several others for whom the summary justice handed out to the respected Ochoa still rankles.

But he does enjoy the support of several of the country's most senior politicians and Communist Party loyalists. Among them are 'economy czar' Carlos Loge, vice-president of the council of state, and Felipe Perez Roque, Cuba's foreign minister. Both are considered likely candidates for the presidency when the Castro era is finally over.