For more than half a century, Cuban leader Fidel Castro has been a target for many of his political enemies and adversaries that tried to topple the socialist regime in the island country by any means, including his assassination.

Castro once stated, in regards to the numerous attempts on his life, that he believed he had set a world record.

"If surviving assassination attempts were an Olympic event, I would win the gold medal," he said.

During his 47 years in power, Castro survived 637 conspiracies to kill him and 164 real assassination plots, making him the most targeted head of state in the 20th century.

"In the last few years, several Cuban security researchers conducted an investigation and we concluded that 637 conspiracies to kill Fidel Castro had been carried out with various methods," Pedro Etcheverry, an investigator at Cuba's State Security Research Center, told Xinhua.

Etcheverry said US intelligence services admitted in 1975 that they had organized eight separate plots to kill Castro since 1960, after he broke off relations with Washington and established key political and economic alliances with the former Soviet Union.

"These plots were never carried out because our security forces dismantled them but it shows how the US tried to physically eliminate Fidel because he was a threat to their interests in Cuba," added the academic.

The expert said the US and anti-Castro groups were very "aggressive" in the early years of the revolution and plots were continuously organized.

He said many factors, including luck, had helped the fact that none of the assassination attempts against Castro were ever successful.

From sniper and bazooka attempts to guns hidden in video cameras and even poisoning milkshakes or chemical attacks to remove his beard have been some of the assassination methods.

One of the most renowned plots was in Chile in 1971 when Fidel Castro visited his ally, former president Salvador Allende.

"During a press conference, the CIA had infiltrated two cameramen with guns inside their video cameras. Minutes before Fidel came out to speak to the press, one of the two men declined to take a shot at Cuba's president and the other one also backed down," said Etcheverry.

Another tense moment came in 1997 in Venezuela when Fidel Castro attended the VII Iberoamerican Summit and terrorist groups planned a disastrous assassination plot.

"The plan in Margarita Island, Venezuela, was to fire a bazooka at Fidel's airplane when it was about to land. The perpetrators were arrested and two bazookas, an assault rifle as well as explosives and guns were found," he added.

Etcheverry believes Castro's enemies never gave up in their attempts to physically eliminate him until he officially retired in 2008.

"The US government and terrorist groups insisted on trying to kill Fidel because he is a symbol of social justice, sovereignty and independence for Cuba and many other nations around the world," he said.