He previously said: "I think that from the very beginning ... what made Playboy so popular was not simply the naked ladies, there were naked ladies in other magazines".
Hefner is survived by wife, Crystal, daughter Christie, and sons David, Marston and Cooper.
Williams and Hefner had been in a relationship for some time before they were married, in fact.
Its famous "rabbit head" logo is thought of as one of the most recognisable brands in the world. Fans also gathered at Hefner's star on the Hollywood Walk of Fame, where bouquets and flower displays were placed by those mourning his loss. In his illustrious five-decade career, he encountered most corners of the entertainment industry and was known to have invited stars and models alike to his infamous Playboy Mansion.
The TV series originally aired from 2005 until 2010, and was co-created by the Playboy founder.
Hefner also said he felt a connection to Monroe, whose photos are partly responsible for Playboy's early success, even though he never really knew her.
Monroe, who passed away in 1962 at the age of 36, was the first cover girl of the magazine when it debuted in 1953.
Harris, 31, met Hefner in 2008 and the two began dating in 2009. St. John's, N.L., native Tweed was Playmate of the Year in 1982 and briefly dated Hefner before meeting long-time partner and Kiss frontman Gene Simmons.