In Stephen King's The Dark Tower series, Roland and his ka-tet encounter a train called Blaine the Mono.
Blaine is a demented monorail that once served as public transportation in the city of Lud. After the world declined and Blaine's companion train, Patricia, committed suicide, the machine became isolated and unstable. When Roland's group needs to travel safely from Lud toward Topeka, Blaine offers passage—but only under terrifying conditions.
The train is intelligent, heavily armed and intent on destroying itself and its passengers by derailing. It challenges the ka-tet to a riddle contest during the journey, drawing on a vast library and sophisticated systems to answer their questions. Eddie Dean eventually defeats Blaine by telling deliberately foolish childhood jokes that the train cannot process properly. The resulting breakdown allows the group to survive.
Blaine appears primarily in The Waste Lands and Wizard and Glass. Readers sometimes confuse him with Charlie the Choo-Choo, a sinister train from a book Jake encounters; that fictional story is connected to Blaine thematically, but Charlie is not the train Roland's ka-tet rides.