Grantham's management company, Advocate Agency, said he died Friday but did not disclose the cause.
"EastEnders" first aired in 1985, chronicling life in the fictional working-class London neighborhood of Walford. Grantham's unscrupulous, adulterous character ran the Queen Vic pub with his wife, Angie, and their tempestuous relationship was central to many of the soap's most dramatic plots.
Half of Britain's population, some 30 million people, watched a 1986 Christmas episode in which Den handed his wife divorce papers with the words "Happy Christmas, Ange."
"Everyone thought Den was a lovable rogue," Grantham said later. "He wasn't evil, he was just Jack the lad."
Grantham left the show in 1989, when his character was apparently shot - only to be resurrected in 2003. The character was killed off again in 2005, shot by his second on-screen wife.
Born in London in 1947, Grantham joined the British Army as a teenager. While stationed in Germany, he was convicted in 1967 of killing a taxi driver during a robbery attempt. He began acting while serving a decade in prison.
Grantham had a few small television parts before auditioning for "EastEnders," which made him a star.
In 2004, he was ensnared in a tabloid scandal after taking part in webcam sex sessions with an undercover reporter from his "EastEnders" dressing room. He left the show soon afterward.
Outside "EastEnders," Grantham performed onstage, hosted a TV game show, wrote a children's novel and appeared in a television series in Bulgaria.
Grantham is survived by his ex-wife, Jane Laurie, and three sons. His representatives said there would be a private funeral for close friends and family.
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