Blaine the Mono was a major antagonist in Stephen King's The Dark Tower Series. He was a pink train (mono-rail). Blaine made appearances in The Waste Lands and Wizard and Glass. He was alone so long that it drove him mad, and he even killed his counterpart, Patricia the Mono, because she complained too much. He was planning on killing himself before reaching Topeka, and then decided to bring Roland and his ka-tet with him.
Before The Dark Tower Series
Blaine was a monorail developed by the Old Ones, with dipolar computers housed under Lud. His original purpose was to house passengers to Topeka, making stops in Candleton, Rilea, The Falls of the Hounds, and Dasherville.
His top speed was 900 miles an hour. Even though he existed in Mid-World he still knew information on the Americas.
He assisted in Patricia's death by removing part of her programming. During his slope into insanity, Blaine developed a rogue part of his brain that was dubbed "Little Blaine". Little Blaine was fearful of the much more dominate "Big Blaine" and wanted to stop him, but couldn't.
Owing to the sometimes mundane, sometimes mystic flow of information between the worlds of The Dark Tower series, a children's book existed on the worlds of Eddie, Susannah and Jake called 'Charlie The Choo-Choo', and both Susannah and Eddie recalled it from their childhoods. The book involved the title train, sentient as Blaine was, and its desire to 'be a happy choo-choo' until the day he died. In illustrations from the book (shown in higher-end editions of DT novels), the children riding aboard Charlie seemed not happy as described, but terrified. Roland noted several portents in the book on several levels, but for then and there shrugged them off as something they would have to keep in mind but act on when the time was right. Somehow, the fanciful story retold the life of Blaine The Mono, though whether this was information the author received through dreams or visions, or if she was a traveler from a world where Blaine existed, is never made clear. The title contains the series' signature 19 letters and was written (or listed as being written by Claudia Bachman, wife of author Richard Bachman, a one-time pseudonym for Stephen King himself. The chills the book gave the ka-tet would prove worth it, preparing them in a broad way to deal with Blaine.
The Waste Lands
Eddie and Susannah found Blaine resting in The Cradle of Lud. When Roland, Jake and Oy reunited with Eddie and Susannah, Blaine had already started releasing nerve gas in Lud. Before the group could board Blaine, they had to solve a riddle, which Susannah did before the gas reached them. While on Blaine, he informed them that he was planning suicide, and he was going to drop of the rails at Topeka, with the ka-tet on him.
Roland asked Blaine to spare them, if they could give Blaine a riddle that he could never solve.
Wizard and Glass
Blaine answers every riddle the group can give him, without pausing. He knows the answer to every riddle. It is only through Eddie's goofy riddles, that Roland deemed "unworthy", that the group was saved. Blaine grew furious, as the answers to Eddie's riddles were so bizarre, and in the end his brain was fried. His body continued to move towards Topeka. He crashes there, but luckily his speed decreased enough that the ka-tet could jump off in time.