Espin died Monday afternoon after "the long illness she was afflicted with" worsened in recent weeks, according to Cuban state television. Authorities did not disclose the illness, but she was said to suffer from severe circulatory problems in recent years.
Her death was likely to have a profound emotional impact on both Raul and Fidel Castro at a critical moment in Cuban history. Not only was she a wife and a sister-in-law, but a fellow guerrilla fighter who was with the Castro brothers at the start of their revolutionary battle a half-century ago.
Cuba's top leaders will pay homage to Espin with a solemn gathering Tuesday night at the Karl Marx theater in Havana, along with leaders of the Federation of Cuban Women and other representatives of Cuban society.
An official mourning period was declared from 8 p.m. Monday until 10 p.m. Tuesday, and the Cuban flag will be lowered to half mast at all public buildings and military bases. Formal gatherings to pay homage to Espin were scheduled for all day Tuesday across the island of 11.2 million. Her ashes will be scattered during a private ceremony, with full military honors, at a date to be determined, according to the statement from Cuba's Communist Party leadership.
"Her name will be linked eternally to the most significant achievements of Cuban women through the Revolution," the government said, calling Espin "one of the most relevant fighters for women's emancipation in our country and in the world."
Born into a wealthy family in eastern Cuba, Espin became a young urban rebel after Fulgencio Batista took power in a coup, and she battled his dictatorship throughout the 1950s.
After the 1959 revolution, she became Cuba's low-key first lady as the wife of Defense Minister Raul Castro, Fidel Castro's designated successor, because Fidel Castro was divorced.
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 and his current marital status is unclear.
Raul Castro, 76, has been Cuba's acting president since 80-year-old Fidel ceded power in July after the first of several surgeries from which he is still recovering.
Espin's power also was rooted in the more than four decades she served 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 in Cuba and at the Massachusetts Institute of Technology, Espin participated in early street protests against Batista, and 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.
Espin sought refuge in 1958 in the mountains above Santiago, where Raul and Fidel Castro commanded their uniformed rebel fighters.
Espin and Raul Castro were married in April 1959, four months after Batista fled the island and rebels marched triumphantly into Santiago, and later Havana. Pictures in Life magazine showed the bride in an elegant white gown and pearls in her hair. The groom was clad in his olive green military uniform, pistol at his side.
Although rumors circulated for years that Espin and Raul Castro had separated, they were often seen together and there was never any official word of divorce.
"Vilma and I sometimes argue," Raul Castro said in April 2001, with his wife at his side. But, he said, "this marriage ... has lasted 42 years, and we hope to be together longer."
Espin's survivors include the couple's four children, Mariela, Deborah, Nilsa and Alejandro, as well as numerous grandchildren.