Mario Chanes de Armas, who was at Fidel Castro’s side in the Cuban revolution only to spend three decades as a political prisoner in the dictator’s jails, has died in a Florida hospital. He was 80.

Chanes de Armas had been in a nursing home but fell ill Saturday and died at Hialeah Hospital.

Chanes de Armas joined Castro during the 1953 attack that began the Cuban revolution. He was sentenced with Castro and others to 15 years by the Batista dictatorship, though they were granted amnesty and released 20 months later.

Soon after, they organized the insurrection which brought them to power in 1959. But Chanes de Armas joined the opposition to the new regime after he became convinced Castro was betraying the democratic promises he had made.

On July 17, 1962, Chanes de Armas was sentenced to 30 years by Castro.

Often kept in horrible conditions, Chanes de Armas and other prisoners challenged the regime from within prison by starting hunger strikes.

Eventually, he and four other prisoners, including Oviedo, were released with the efforts of several human rights organizations and his family, who had met with President George H.W. Bush.

Chanes de Armas served as one of the directors of Grupo Plantados, meaning those who refuse to budge.

He later traveled to Washington in 1993, where he was received by then-President Clinton.

“He sacrificed the best years of his life to the ideal that he and his fellow citizens will be free,” Mr. Clinton said in a statement. “It is men and women like him who have built our land into a beacon of freedom and hope for the oppressed peoples of the world.”