But despite rumors that he was in poor health, the bearded revolutionary has shown in recent weeks he still has the energy to give his traditional hours-long speeches and keep up a work schedule that would exhaust a much younger man.
He also remains as defiant and independent as ever.
"Cuba does not need the help of the European Union to survive," Castro told an enthusiastic crowd of about 10,000 supporters in the eastern city of Santiago on July 26 as he celebrated the 50th anniversary of the start of the Cuban revolution.
Fidel Castro Ruz was born in eastern Cuba's sugar country, where his Spanish immigrant father ran a prosperous plantation. His official birthday is Aug. 13, 1926, although some say he was born a year later.
No official celebrations of the leader's birthday were announced. Castro usually keeps the occasion low-key, sometimes sharing a cake with Cuban schoolchildren.
Still, Cuba's official media was filled Wednesday with birthday greetings.
"A giant kiss from the grandson who loves you so much," the child Elian Gonzalez wrote in a letter published in Juventud Rebelde, the communist youth newspaper. Elian was 6 years old in 2000 when Castro led a successful international campaign to return the boy from his relatives in South Florida to his father on the island.
The international custody focused American attention on the island that later led to attempts to ease U.S. trade and travel sanctions against Cuba.
But Castro began losing some of his former friends this spring when his government launched a crackdown on the opposition, jailing 75 dissidents and sentencing them to prison terms of up to 28 years.
It was the firing-squad executions of three convicted ferry hijackers during that same period that especially troubled some of Castro's foreign supporters.
Even some formerly sympathetic intellectuals on the left expressed disappointment, among them Uruguayan author Eduardo Galeano, who once praised Castro as a "symbol of national dignity."
"Must they learn the bad habits of the enemy they are fighting?" Galeano wrote, criticizing the executions.
Cuba later justified its use of the death penalty to halt a brewing emigration crisis.
When the European Union expressed concern about the April 11 executions and the crackdown on dissidents, Castro mocked the prime ministers of Spain and Italy as "fascists" and led huge protests outside those countries' embassies here.
During his July 26 speech, Castro said Europe should be ashamed of its past, and said EU members were "a group of old colonial powers historically responsible for slave trafficking, looting and even the extermination of entire peoples."
The EU is Cuba's largest trade, aid and investment partner. It opened an office in Havana earlier this year — before the crackdown and the executions — to administer the up to $16.4 million in aid it has given Cuba each year.
After Castro said he didn't want the money, the EU said it was still willing to help.
With Cuba's current economic situation, it can ill afford to lose any foreign trade or aid.
Castro's government is struggling with a severe cash crisis, despite a recent jump in the number of visitors to the island following a tourism slump following the Sept. 11, 2001 terrorist attacks on the United States.
This year's sugar harvest — another important source of foreign currency — brought in only about 2.2 million tons, by far the lowest figure in decades. The last two annual harvests ranged between 3.5 and 3.6 million metric tons.
Nevertheless, Castro remains firmly in control after nearly 45 years as the president of the Council of State, president of the Council of Ministers and first secretary of the Communist Party of the only communist state in the Americas and one of only four in the world.
When Cuba's rubber-stamp parliament confirmed him in March to a sixth term as the island's maximum leader in March, Castro acknowledged he won't be around forever. His current five-year term would have him governing until he is 81.
"I promise that I will be with you, if you so wish, for as long as I feel that I can be useful — and if it is not decided by nature before," Castro said at the time in a rare reference to his advancing age and mortality. "Not a minute less and not a second more.
"Now I understand that it was not my destiny to rest at the end of my life," he added.