Captain Homero Cesar Machado was 75. He died Thursday and his body was cremated Friday in Sao Paulo, the reports said.
Rousseff, a one-time Marxist guerrilla, was tortured by the military dictatorship that ruled Brazil from 1964 to 1985.
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She told Folha de Sao Paulo newspaper in a 2005 interview that Machado was one of her tormenters during her imprisonment in the 1970s.
A truth commission that carried out a nearly three-year investigation on crimes committed by the military regime accused Machado of directing the torture of Rousseff and three others.
Unlike its South American neighbors, Brazil has not prosecuted military officials for regime-era crimes because of a 1979 amnesty law ratified in 2010.
The truth commission found that the country's military dictatorship killed or disappeared at least 434 people.
Brazil has officially recognized some 400 deaths or disappearances under the military regime -- compared with 30,000 deaths in neighboring Argentina and more than 3,200 in Chile.
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Rousseff created the truth commission in 2011 shortly after taking office.
The country's first female president is now facing a likely impeachment trial over accusations of illegal accounting maneuvers to mask the depth of Brazil's economic troubles during her tight 2014 reelection victory.
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