The Dark Tower is a series of eight books which span an entire connected universe which links several other books and stories by Stephen King, including Bag of Bones, The Talisman, Black House, The Stand, Everything's Eventual, From a Buick 8, Hearts in Atlantis, Insomnia, The Eyes of the Dragon and 'Salem's Lot, with minor references to IT, The Mist and The Shining.

Dr. Hotchkiss, Jake's psychiatrist, has a picture in his office of the Overlook Hotel, from The Shining (1980), another film based on a Stephen King novel.

According to an introduction by Stephen King in one of his books, The Good, the Bad and the Ugly (1966) along with the "Lord of the Rings" book series, is the primary influence for his book series: "The Dark Tower".

Daniel Craig, Christian Bale, Viggo Mortensen, Javier Bardem and Mads Mikkelsen were considered for the lead role before Idris Elba was cast.

During the first act of the film, several Stephen King Easter eggs are visible. The twins from The Shining (1980), the family (including the dog) from Cujo (1983), and the car from Christine (1983) (as the toy pushed by Jake in his room) are each shown briefly.

Was originally to be adapted to film by J.J. Abrams following his success with the Lost (2004) television series. After Abrams backed out, Ron Howard became attached to the project until the rights went to Nikolaj Arcel.

Based on Stephen King's "Dark Tower" series of novels, which was inspired in part by Robert Browning's poem "Childe Roland to the Dark Tower Came".

The Dark Tower is 182 meters/600 feet tall, stands in the eastern land known as End World, is surrounded by a field called Can'Ka No Rey, and is held together by six beams that stretch to the corners of the land and are guarded by twelve massive beasts on each end.

Nicholas Hamilton plays minor character Lucas Hanson. Hamilton also stars in Stephen King's It (2017) as Henry Bowers. An abandoned theme park appears in the Dark Tower, with a sign that says 'Pennywise', along with a balloon sculpture. Pennywise is the clown villain from IT, and appears with balloons in the novel and movie.

Early publicity stills reveal Easter eggs for Stephen King fans, including a shop sign for "Barlow and Straker's". Barlow was the vampiric villain in "Salem's Lot", with Straker being his assistant.

The chime that plays in the first official trailer is the same one that plays in the two pocket watches in 'For a Few Dollars More", the 1965 Spaghetti Western that teams up Clint Eastwood and Lee Van Cleef as two bounty hunters chasing a vicious gang. They then starred as antagonists in 'The Good, The Bad, and the Ugly" (1966). Stephen King claims that movie was half the inspiration for 'The Dark Tower'.

After poor test screenings, Sony spent $6m on re-shoots to help flesh out Idris Elba's Gunslinger character.

During one of Jake's visions at the beginning of the film, he hears the phrase "The man in black fled across the desert, and the gunslinger followed." This is, word for word, the opening line of the first book in the Dark Tower series.

Tom Hardy was considered for the role of the Man in Black.

More references to other Stephen King books were planned, but were scaled back as it became clear that the copyright issues would have taken years to figure out

When Abbey Lee entered talks to appear as the "female lead" of Tirana, it caused some confusion among fans of the book series, as the character was originally written as a minor villain with little influence on the plot and does not appear until the final book in the series.

Roland sees a TV commercial with talking raccoons and asks Jake if 'animals still talk here'. This is a nod to the character Oy in the books; a talking raccoon-like creature called a Billy Bumbler who Jake befriends.

When Jake is wandering the forest he stumbles across a carnival ride bearing the name "Pennywise", who is the primary antagonist in Stephen King's novel "It".

The original Dark Tower book series was 7 novels.

In an interview with Collider, King expressed hope for a sequel film in addition to the television series, suggesting that it should be R-rated, have Roland wearing a hat, and include the "lobstrosities" from The Dark Tower II: The Drawing of the Three. In an interview with Coming Soon, Arcel confirmed that The Drawing of the Three would form the basis for the sequel, and that Eddie and Susannah would appear alongside Elba, McConaughey, Taylor and Haley reprising their roles as Roland, Walter, Jake and Sayre respectively.

Several of Stephen King's other novels are connected to the Dark Tower series, and some of them have been adapted into films. They have all featured actors from the various Star Trek series. The earliest novel with such a connection was Salem's Lot. The first film adaptation featured Julie Cobb, who appeared in the original Star Trek series. The 2003 remake featured Cobb's former husband, James Cromwell, who played the crossover character Father Callahan, and had appeared in First Contact (1996). The Stand (1994) featured Ray Walston, who appeared on an episode of Star Trek: The Next Generation (1987); and Miguel Ferrer, who appeared in Star Trek III: The Search for Spock (1984). Hearts in Atlantis (2001) featured Anton Yelchin, whose final film role was in Star Trek Beyond (2016), opposite Idris Elba.

Idris Elba appeared the previous year in Star Trek Beyond (2016) opposite the late Anton Yelchin. Yelchin had appeared in Hearts in Atlantis (2001), which was also based on a Stephen King novel with connections to the Dark Tower series: Anthony Hopkins's character appears in the final novel of the series, and notes that Jake Chambers could easily have been a "twinner" for Bobby Garfield. Elba also appeared opposite Hopkins in Thor (2011).

Roland Deschain (Idris Elba) is told in New York hospital that he has chronic radiation poisoning. In Pacific Rim (2013), Idris Elba's character Stacker Pentecost also has to take pills to manage his radiation poisoning.

The movie adaptation has recently been revealed to be a sequel to The Dark Tower book series. The movie will begin where the books technically end, now with Roland beginning his quest once again, only this time with the 'Horn of Eld' in his gunna.

Stephen King's 'Dark Tower' novels connect many other novels into a single fictional universe. Walter O'Dim, AKA The Man in Black, is later revealed to use the alias Randall Flagg (Jamey Sheridan), under which guise he caused the events of The Stand (1994). The fourth novel, Wizard and Glass, involves Roland and his ka-tet traveling to the world in which The Stand takes place. Father Callahan, the Catholic Priest from Salem's Lot (1979) appears in the last three books in the series. The last book features appearances by Ted Brautigan, the character played by Anthony Hopkins in Hearts in Atlantis (2001), and Dinky Earnshaw, the character played by Michael Flores in Everything's Eventual (2009). Another character from the final book, Patrick Danville, first appears as a toddler in the novel Insomnia, which has not been filmed. The alternate universe in which the Dark Tower novels take place is also the setting of The Talisman and its sequel Black House.

In The Mist (2007) a poster of a fictional movie based on The Dark Tower can be seen in the house of David Drayton (Thomas Jane). It appears when Drayton is doing a picture of Roland Deschain, played in this movie by Idris Elba. It should be a clue for an imminent movie about The Dark Tower, but the failure of the film delayed the project during several years.

Variety reported that Sony and MRC spent $6 million on reshoots to fill in more backstory about Idris Elba's character's hatred for Matthew McConaughey's Man in Black. In addition, to better familiarize audiences with Mid-World, the film's magical setting, five minutes of exposition were cut and a new scene was shot to combine ideas that had been sprinkled throughout the picture.

The main antagonist of the series, the Crimson King, only makes a brief appearance at the conclusion of the last novel. If you pause the trailer for this movie at the 1:50 mark you can see that the wall The Man In Black walks by has "All Hail The Crimson King" painted in red on it.

The code for the portal to return to the village was 1408, as an Easter egg to Stephen King's other story "1408".

The Man in Black uses both, a pink and a black orb. In the novels these spheres are referred to as "Maeryln's Grapefruit" and "Black 13" respectively. They are part of "Maeryln's Rainbow" a group of 13 magical spheres each representing the beams holding up the Dark Tower, Black 13 representing the Tower itself.

During their final confrontation, the Man in Black taunts Roland by saying the quest for the Tower always leads back to him. This is a subtle reference to the seventh Dark Tower book, where it's revealed that Roland has in fact reached the Tower on multiple occasions, and is sent back to the beginning of his quest, hunting the Man in Black, each time.

The infamous character of Stephen King makes an appearance in the last two novels (Song of Susannah, and the Dark Tower).

When the Gunslinger is fighting the Man in Black at the gun shop, the poster of Rita Hayworth can be seen. This is a nod to the novella Rita Hayworth and the Shawshank Redemption, that movie was adapted from.

The Man In Black's ominous whistle can be heard after the credits roll, suggesting that he may still be alive.

Callouts to other books and events in the series include: The opening titles include a title card for the "Tet Corporation" with a logo featuring a turtle. There's a rose on left of the turtle's shell. Maerlyn's Rainbow: Walter opens a cabinet containing rows of colored glass spheres. He uses one to track Jake, and another (Black Thirteen) to communicate with and taunt Roland from afar. Charlie the Choo Choo: Jake and Roland camp in an abandoned theme park in mid-world, and as Jake walks by a roller coaster for small children you can see the leading car of the coaster has a huge grinning face. Rose: In the final scene of the film, Roland and Jake enter a building with a large graffiti Rose on the front, next to "King Jewelers".

To most die-hard fans of the Stephen King novels (mainly The Stand and The Dark Tower series), The Man in Black is an incarnation of the Walkin' Dude, also known as Randall Flagg. Matthew McConaughey was originally considered to play a character in Josh Boone's upcoming adaptation of 'The Stand (I)', and according to the information, he was to play the heroic character from Arnette, Texas: Stu Redman, instead of Randall Flagg. However, since Randall/Walter/Marten can change his appearance seemingly at will through his black magic, it is possible that he can be played by multiple actors.

Shortly after Jake meets Roland in Mid-World, they start walking and Jake slips on the edge of a cliff. In the first novel, The Gunslinger, Roland lets Jake fall off a cliff in pursuit of The Man in Black. In the film he threatens Jake with falling off of a cliff, but he does not fall.

During Jake's therapy session, there is a picture on a table of The Overlook Hotel, an homage to another King novel, The Shining.

The official poster of the movie features Gunslinger and Jake Chambers on foot of the image, on an upside-down New York, with the Man in Black walking by an equally upside-down street at the head of the image. This upside-down and white New York's skyline foreshadows the appearance of the Dark Tower.