Randall Flagg is a fictional character created by American author Stephen King, who has appeared in at least nine of his novels. Described as "an accomplished sorcerer and a devoted servant of the Outer Dark", he has supernatural abilities involving necromancy, prophecy, and influence over animal and human behavior. His goals typically center on bringing down civilizations through destruction and conflict. He has a variety of names, usually with the initial letters "R. F." but with occasional exceptions, such as Walter o'Dim and Marten Broadcloak in The Dark Tower series.

The Dark Tower is a series of eight novels, one novella, and a children's book written by American author Stephen King. Incorporating 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.