Four decades ago he had executed Che Guevara at the instance of Americans.
Che dead has been a tremendous source of inspiration for many fighting for underdogs the world over and is a national hero for Cubans.
All the same in a striking display of forgiveness, Cuban doctors have saved the sight of the very man who took away the life of their idol.
He had cataracts removed under a Cuban programme to offer free eye treatment across Latin America.
Cuban media reported news of the surgery ahead of the 40th anniversary of Che's death on 9 October.
The operation on Mr Teran took place last year and was first revealed when his son wrote to a Bolivian newspaper to thank the Cuban doctors for restoring his father's sight.
But Cuban media took up the story at the weekend as the island prepares for commemorations to mark Che Guevara's death in 1967.
"Four decades after Mario Teran attempted to destroy a dream and an idea, Che returns to win yet another battle," the Communist Party's official newspaper Granma proclaimed.
"Now an old man, he [Teran] can once again appreciate the colours of the sky and the forest, enjoy the smiles of his grandchildren and watch football games."
Che Guevara, who played a key role in the Cuban revolution of 1959, travelled to Bolivia in 1966 to start a social revolution.
But in October 1967, the Bolivian army, with assistance from the CIA, captured Guevara and his remaining fighters.
Che Guevara, wounded in the fighting, was taken to a schoolhouse in the village of La Higuera on 8 October where the soldiers debated what to do with him.
Mario Teran is reported to have drawn the short straw and been ordered to execute the captured guerrilla.
Che Guevara was killed on 9 October and his body taken to a hospital in nearby Vallegrande, where his corpse was paraded before the world's media.
In 1997 his remains were discovered, exhumed and returned to Cuba, where he was reburied.