Vilma Espin Guillois, the wife of acting President Raul Castro and one of the communist nation's most politically powerful women, died Monday, the Cuban government announced. She was 77.

As Raul Castro's wife, Espin was Cuba's de facto first lady for decades because Cuban leader Fidel Castro is divorced.

Cuban state television announced Espin died at 4:14 p.m. Monday following a long undisclosed illness. An official mourning period was declared from 8 p.m. Monday until 10 p.m. Tuesday.

Born into a wealthy family in eastern Cuba, Espin became a young urban rebel who battled against Fulgencio Batista's dictatorship throughout the 1950s. After the 1959 triumph of the Cuban revolution, she became Cuba's low-key first lady as the wife of Defense Minister Raul Castro, Fidel Castro's designated successor.

Both as a Castro family member and a leader in her own right, Espin assumed her first lady duties shortly after the revolutionary triumph.

Espin maintained that role over more than 45 years, even after Fidel Castro reportedly married Dalia Soto del Valle, with whom he is said to have five grown sons. Extremely protective of his private life, Fidel Castro has never discussed that relationship publicly.

Espin's power also was rooted in more than four decades as president of the Federation of Cuban Women, which she founded in 1960 and fashioned into an important pillar of support for the communist government. Virtually every woman and adolescent girl on the island are listed as members.

A tall woman with spectacles, her auburn hair twisted into a bun, Espin was a highly recognized figure across the island. She was regularly seen at gatherings of the National Assembly and other important government meetings.

Born in Santiago on April 7, 1930, and trained as a chemical engineer, Espin participated in early street protests against Batista, who seized power in a 1952 coup.

She later became deeply involved in the revolutionary underground, working with regional leader Frank Pais, who was assassinated in July 1957. Even before Pais died, Espin had assumed leadership of the urban rebel movement in eastern Cuba.