Question: How many books are in the Stephen King series of which Roland Deschain of Gilead is the protagonist?

Context articles: The Dark Tower: Battle of Jericho Hill
Roland Deschain
The Dark Tower V: Wolves of the Calla
The Dark Tower (series)
Storm of the Century
Robin Furth
Unpublished and uncollected works by Stephen King
The Dark Tower II: The Drawing of the Three
The Dark Tower (2017 film)
No entren al 1408

The Dark Tower: Battle of Jericho Hill is a five-issue comic book limited series published by Marvel Comics.
 It the fifth comic book miniseries based on Stephen King's "The Dark Tower" series of novels.
 It is plotted by Robin Furth, scripted by Peter David, and illustrated by Richard Isanove and Jae Lee.
 Stephen King is the Creative and Executive Director of the project.
 The first issue was published in December 2009.
 The series tells the developments leading to the final battle between the gunslingers of Gilead and the forces of John Farson's rebellion.
Roland Deschain of Gilead is a fictional character and the protagonist of Stephen King's "The Dark Tower" series.
 He is the son of Steven and Gabrielle Deschain and is descended from a long line of "gunslingers", peacekeepers and diplomats of Roland's society.
Wolves of the Calla is the fifth novel in Stephen King's "The Dark Tower" series.
 This book continues the story of Roland Deschain, Eddie Dean, Susannah Dean, Jake Chambers, and Oy as they make their way toward the Dark Tower.
 The subtitle of this novel is "Resistance".
 Prior to the novel's publication, two excerpts were published: "Calla Bryn Sturgis" was published in 2001 on Stephen King's official site, and "The Tale of Gray Dick" was published in 2003 in "McSweeney's Mammoth Treasury of Thrilling Tales".
 Both excerpts were incorporated in revised form into the novel.
 "Wolves of the Calla" was nominated for the Locus Award for Best Fantasy Novel in 2004.
The Dark Tower is a series of eight books written by American author Stephen King that incorporates themes from multiple genres, including dark fantasy, science fantasy, horror, and Western.
 It describes a "gunslinger" and his quest toward a tower, the nature of which is both physical and metaphorical.
 The series, and its use of the Dark Tower, expands upon Stephen King's multiverse and in doing so, links together many of his other novels.
 King has described the series as his "magnum opus".
 In addition to the eight novels of the series proper that comprise 4,250 pages, many of King's other books relate to the story, introducing concepts and characters that come into play as the series progresses.
Storm of the Century, alternatively known as Stephen King's Storm of the Century, is a 1999 horror TV miniseries written by Stephen King and directed by Craig R. Baxley.
 Unlike many other King mini-series, "Storm of the Century" was not based upon a Stephen King novel—King wrote it as a screenplay from the beginning.
 The screenplay was published in February 1999.
Robin Furth was the personal research assistant to Stephen King and the author of Stephen King's "The Dark Tower: A Complete Concordance", which was published by Scribner on December 5, 2006.
 It is a compilation of her two previous encyclopedic books dealing with King's magnum opus, "The Dark Tower: A Concordance, volume I" - which explores the first four books in King's series - and "A Concordance II", which gives the reader definitions and explanations of pivotal terms used over the course of the final three books of The Dark Tower.
 She is now currently working on the graphic novel adaptation of the Dark Tower for Marvel Comics .
According to books by Tyson Blue ("The Unseen King"), Stephen J. Spignesi ("The Lost Work of Stephen King"), and Rocky Wood "et al." ("Stephen King: Uncollected, Unpublished"), there are numerous unpublished works by Stephen King that have come to light throughout King's career.
 These allegedly include novels and short stories, most of which remain unfinished.
 Most are stored among Stephen King's papers in the special collections of the Raymond H. Fogler Library at the University of Maine, some of which are freely accessible to the library's visitors.
 However, others require King's permission to read.
 Additionally, there are a number of uncollected short stories, published throughout King's long career in various anthologies and periodicals, that have never been published in a King collection.
The Drawing of the Three is a fantasy novel by American writer Stephen King, the second book in "The Dark Tower" series, published by Grant in 1987.
 The series was inspired by "Childe Roland to the Dark Tower Came" by Robert Browning.
 The story is a continuation of "" and follows Roland of Gilead and his quest towards the Dark Tower.
 The subtitle of this novel is RENEWAL.
The Dark Tower is a 2017 American science fantasy western film directed and co-written by Nikolaj Arcel.
 A continuation of Stephen King's novel series of the same name, the film stars Idris Elba as Roland Deschain, a gunslinger on a quest to protect the Dark Tower—a mythical structure which supports all realities—while Matthew McConaughey plays his nemesis, Walter Padick, the Man in Black, and Tom Taylor stars as Jake Chambers, a New York boy who becomes Roland's apprentice.
No entren al 1408: Antología en español tributo a Stephen King (English: "Do Not Enter Room 1408: A Spanish Anthology Tribute to Stephen King") is a collection of horror stories by 22 Spanish-language authors, which aims to pay tribute to the style of the horror master Stephen King.
 The book was edited by the Ecuadorian writer Jorge Luis Cáceres.
 These books entitled “No entren al 1408” (Don’t enter the 1408) and “King, tributo al rey del terror” (King, tribute to the king of terror, InterZona, Buenos Aires, 2015), have three editions: Ecuador, 2013; Mexico, 2014 and Argentina, 2015, and are written by 30 writers from: Chile, Cuba, Ecuador, Mexico, Argentina, Uruguay and Spain.