As the late Cuban leader's ashes are laid to rest in the eastern city of Santiago de Cuba on Sunday, his cause of death remains a closely-guarded state secret.
Castro claimed he was the target of some 600 assassination plots, but it appears likely that it was simply old age that finally felled the death-defying communist leader. He was 90 and no longer president when he died on November 25.
CIA documents and a report by the US Senate's Church Committee in 1975 reveal plots that were cooked up by spooks, including some that never left "the laboratory phase.
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Depilate 'The Beard'
Some early schemes didn't even involve murdering Castro and seemed more like elaborate high school pranks.
The Church Committee said that from March to August 1960, "the CIA considered plans to undermine Castro's charismatic appeal by sabotaging his speeches."
One idea involved spraying Castro's broadcasting studio with an LSD-like chemical, but it was rejected because the drug was "unreliable."
The agency's Technical Services Division (TSD) treated a box of cigars with a chemical that produced temporary disorientation, hoping Castro would light up a stogie before a speech and make a fool of himself.
The committee also found a scheme "to destroy Castro's image as 'The Beard' by dusting his shoes with thallium salts" -- a strong depilatory that would cause his famous facial hair to fall out.
The plan was to put the substance in Castro's shoe in case he put them outside his hotel room's door to be shined while in another country, but the Cuban leader cancelled the trip.
In this 1960 file photo, Cuba's revolutionary hero Ernesto "Che" Guevara, center, Cuba's leader Fidel Castro, left, and Cuba's President Osvaldo Dorticos, right (AAP) Source: AAP
Lethal cigar
The Church Committee's report found "concrete evidence of at least eight plots involving the CIA to assassinate Fidel Castro from 1960 to 1965."
A box of Castro's favorite cigars was treated with "a lethal botulinum toxin so potent that a person would die after putting one in his mouth," the Church Committee said.
The cigars were delivered to an unidentified person in February 1961, but "the record does not disclose whether an attempt was made to pass the cigars to Castro."
Mobsters
In 1960, the CIA recruited mafia figures to kill Castro and offered $150,000 if they succeeded.
The agency considered gunning down Castro in a "gangland-style killing," but the mobsters suggested a more discreet method: Slipping a poison pill in Castro's food or drink.
The TSD made a pill containing botulinum toxin, which was given to a Cuban official, Juan Orta.
But after several weeks of attempts, Orta apparently got "cold feet" and abandoned "the assignment," according to a CIA memo.
The poison pill plot was revived after the Bay of Pigs fiasco, but it was abandoned again in 1963.
Explosive mollusk
In 1963, the chief of Task Force W, the CIA section handling covert Cuban operations, asked his assistant to see if "an exotic seashell, rigged to explode" could be placed in a location where Castro went skin diving, according to the committee.
The TSD explored the idea but determined it was "impractical."
Contaminated diving gear
The CIA considered having James Donovan, a US lawyer who was negotiating with Castro the release of Bay of Pigs prisoners, deliver a "contaminated" diving suit to Castro.
The TSD dusted the inside of a suit with a fungus that would cause a chronic skin disease known as Madura foot. The lab also contaminated the breathing apparatus with tubercle bacillus.
But the poisoned gear never left the lab.
Poison Pen
A CIA official gave a high-ranking Cuban official codenamed AM/LASH, who wanted to "eliminate" Castro, a poisonous ballpoint pen rigged with a hypodermic needle "so fine that the victim would not notice its insertion," the committee said.
AM/LASH, later identified as Major Rolando Cubela, was unimpressed, saying the CIA could have "come up with something more sophisticated than that."
A CIA official said he could not remember whether the Cuban threw away the pen or kept it, but AM/LASH stated that he would not take it to Cuba.
In a historical coincidence, the pen was delivered on November 22, 1963 -- the day US President John F. Kennedy was shot in Dallas.
