Most people know Stephen King as the Master of Horror, who has famously created books that have been adapted into films, and works like Carrie, The Shining, Cujo, Firestarter, and Misery. Most of his works are horror, but some of his non-horror works have been adapted into something different such as Shawshank Redemption and The Green Mile. One of King's ongoing series that took decades to finish was The Dark Tower, and the series with its mix of dark fantasy, science fiction, western, and (of course) horror is about to have its first feature film adaptation. This is what is known on Stephen King's The Dark Tower film, and whatever the long-term plan for it could be.
According to IGN, a tweet from the Master of Horror himself states that filming for The Dark Tower has begun. The film has a lot of star power in its cast as Idris Elba (an African-American actor most famous for roles in Thor and Pacific Rim) will be playing the role of The Gunslinger Roland Deschain, a character who was designed after "The Man with No Name" character in Clint Eastwood films. The Gunslinger is chasing down his adversary known as "the man in black", who will be played by Matthew McConaughey.
The film also stars Abbey Lee (Mad Max Fury Road) as Tirana, as well as Jackie Earle Haley as Sayre. Haley has played iconic characters in the past like Rorschach from Watchmen, and Freddy Krueger in the remake of A Nightmare on Elm Street. The film is directed by Nikolaj Arcel (A Royal Affair), who has written the screenplay with King as well as veteran screenwriter Akiva Goldsman (A Beautiful Mind).
The Dark Tower series is what King considers to be his "magnum opus", and it has eight novels in total. The series actually ends with the seventh book, simply called The Dark Tower (2004). There a recent book published in 2012 known as The Wind Through The Keyhole which takes place in between books four and five.
There are many other books that tie-in with the story of The Dark Tower, with a lot of Stephen King concepts and characters. It takes place in a world that is part Old West meets future timeline, perhaps after the events of a nuclear war. The first book of The Dark Tower series, simply called The Gunslinger, was actually a combination of five stories that were originally published in The Magazine of Fantasy and Science Fiction from 1978-1981.
Considering that the series encompasses 4,250 pages, what isn't known is the long-term plan for this series. There is a trend in Hollywood now to green-light film series and not just individual films, but is the plan to make just an adaptation of The Gunslinger, and then see if the numbers will justify the other seven or eight books in the series? If so, that is a mammoth project and the actors for what is probably the first film are in for the long haul.
The Dark Tower will be released into theaters on February 17, 2017. King mentioned in his tweet that production for IT, one of his very long novels that was once a TV mini-series in the early 90's, will soon begin production as well.