Biggs was part of a gang that robbed the mail train from Glasgow to London on August 8, 1963 and escaped with 2.6 million pounds, a record haul at the time.
Although they initially seemed to get away with it, 11 of the robbers were rounded up and sent to jail, with Biggs sentenced to 30 years. But he escaped from Wandsworth prison in 1965 and ultimately reached Rio de Janeiro, Brazil.
There he had a son with his Brazilian girlfriend, which ensured him immunity from extradition to Britain.
Biggs was being cared for at the Carlton Court Care Home in East Barnet, north London. He was last seen in public at the funeral of his fellow Great Train Robber, Bruce Reynolds, in March.
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Anthony Delano, who wrote a book about the robbery, told Sky News that Biggs was an "idiot".
"He was a small time south London crook who nobody wanted on the team because he was a weak link," Delano said.
"I am equally happy to be described as the 'tea-boy' or 'The Brain'. I was there that August night and that is what counts. I am one of the few witnesses - living or dead - to what was 'The Crime of the Century'," he said.
Christopher Pickard, ghost writer of Biggs's autobiography, said he should be remembered as "one of the great characters of the last 50 years".