Which C.S. Lewis book was first published in 1942 as letters from a demon?

The Screwtape Letters was first published in 1942 as letters from a demon.

The book is a fictional series of letters written by Screwtape, a senior demon, to his inexperienced nephew Wormwood. Screwtape offers advice about tempting a human patient, allowing Lewis to discuss moral psychology, spiritual distraction, pride, and self-deception from an intentionally inverted viewpoint.

Lewis wrote the work during the Second World War, and its unusual form made difficult theological ideas accessible to a broad readership. The letters first appeared in the Anglican newspaper The Guardian before being collected as a book.

Readers sometimes mistake Screwtape for the devil himself, but the character is a senior tempter within Lewis’s invented demonic bureaucracy. The book is satire and Christian apologetics rather than a literal account of supernatural correspondence.