Screwtape writes the letters in C.S. Lewis’s 1942 book The Screwtape Letters. The book is presented as a series of instructions from a senior demon to his inexperienced nephew, Wormwood.
Screwtape advises Wormwood on how to tempt a human patient. Lewis uses the inverted viewpoint to satirize habits such as self-deception, distraction, pride, and resentment. The humor comes from allowing a demon to describe destructive behavior as professional strategy.
The work began as a series of letters published in the Anglican newspaper The Guardian. Lewis later collected them as a book in 1942, and the volume became one of his best-known works of Christian apologetics and satire.
The names can be easy to reverse. Screwtape is the older adviser and letter writer; Wormwood is the junior tempter receiving the correspondence. The book is fictional, not a literal theological manual about a historical demon.