Hickenlooper was found dead Saturday morning, Denver police told the Associated Press. Denver Mayor John Hickenlooper, who is running for governor of Colorado, said in a statement that his cousin died of natural causes.
George Hickenlooper was in Denver for the premiere at a film festival of his latest movie, "Casino Jack," starring Kevin Spacey. The film about former Washington lobbyist Jack Abramoff is scheduled to open in December.
"We are devastated," John Hickenlooper said in a statement. "His passion for life, zeal for people and unquenchable curiosity enriched everyone who had the fortune to know him."
Hickenlooper was born May 25, 1963, in St. Louis and had "a very interesting childhood," he told the St. Louis Post-Dispatch in 2002. His father, George Sr., was a professor and playwright. His mother started a guerrilla theater group after the family moved to Northern California in the late 1960s.
They returned to St. Louis, and Hickenlooper graduated from St. Louis University High. He moved to Los Angeles after graduating from Yale University.
Other films directed by Hickenlooper include "Factory Girl" in 2006, "Mayor of the Sunset Strip" in 2003, "The Big Brass Ring" in 1999 and last year's "Hick Town," based on footage shot while he followed his cousin during the Democratic National Convention in 2008.
"Hearts of Darkness" dealt with the making of Francis Ford Coppola's 1979 film "Apocalypse Now" and first aired on Showtime. Hickenlooper was credited as co-director with Fax Bahr and Eleanor Coppola.
The film meshed footage shot by Eleanor Coppola during the arduous filming of "Apocalypse Now," set during the Vietnam War, with interviews with the Coppolas and the cast and crew.
"I thought that there was a strong parallel between Francis making the movie and the war itself," Hickenlooper told The Times in 1992. "He really delved into the most sordid aspects of his own character in order to accomplish something that, fortunately, ended up being a great piece of art."
Hickenlooper is survived by his wife, Suzanne; and son, Charles, according to the statement from John Hickenlooper.