The "Cuban Five" refers to intelligence agents whose so-called "Wasp Network" operated in Florida in the 1990s. They were arrested in 1998 and later convicted on charges including conspiracy and failing to register as foreign agents.

Cuba insists they were not acting against U.S. sovereignty, only keeping tabs on militant exile groups that Havana blames for terror attacks on the island, including a string of hotel bombings. However, prosecutors argued they also tried to penetrate military bases, including the U.S. Southern Command and facilities in the Florida Keys.

For years, Havana has made them an official cause celebre, rivaling the case of Elian Gonzalez, the boy rafter who in 2000 was caught in a tug-of-war between his Cuban father and family in Miami.

The "Five Heroes," as they are known in Cuba, are fixtures in state media and their faces grace billboards across the island. Schoolchildren are taught their names and take part in public acts demanding their release. However the five are reviled as spies by many exiles in South Florida.

One, Gerardo Hernandez, had been serving a life sentence on charges of murder conspiracy related to the Cuban air force's 1996 shoot-down of two planes flown by Brothers to the Rescue, an exile organization that sought to aid migrants at sea and also dropped propaganda leaflets.

Rene Gonzalez, a dual U.S.-Cuban national, became the first of the agents to walk free in October 2011 after completing about 13 years behind bars. He was initially ordered to serve three years of supervised parole and remain in the United States, but in 2013 a judge allowed him to return to Cuba and renounce his U.S. citizenship.

Fernando Gonzalez, who is not related to Rene Gonzalez, was released in February 2014 after serving more than 15 years, and quickly deported to Cuba. The last three still in American lockups were Hernandez, Antonio Guerrero and Ramon Labanino.