NEW YORK, Aug 1 (Reuters) US author Stephen King played a key role in translating his book series "The Dark Tower" into a Hollywood film, director Nikolaj Arcel said at the film's premiere. The fantasy movie follows the eight-book series in crafting the classic story of good versus evil. Gunslinger Roland Deschain, played by actor Idris Elba, battles his nemesis, the Man in Black, who is determined to destroy the Dark Tower, which holds their universe together. "He was very involved and had a lot of ideas. He never dictated anything, but he always had good opinions," Arcel yesterday said of King's role in bringing the series to the big screen. Actor Matthew McConaughey said he enjoyed portraying the villainous Man in Black. "Bad guys are real fun to play because they are limitless," he said. "They don't pander. They're not trying to make friends. They're not trying to have their manners and graces." "The Dark Tower" opens in US cinemas on August 4. REUTERS SV 0903