Walter Michael Miller Jr. (January 23, 1923 – January 9, 1996) was an American science fiction writer, renowned for his fix-up novel, A Canticle for Leibowitz (1959), which was the only novel published in his lifetime. This notable work won the 1961 Hugo Award for Best Novel. Before this significant achievement, he was known for his short stories.

Miller was born in New Smyrna Beach, Florida, and pursued his education at the University of Tennessee and the University of Texas. His career before becoming a full-time writer included working as an engineer. During World War II, he served in the Army Air Corps as a radioman and tail gunner, completing more than fifty bombing missions over Italy. One of his missions included the bombing of the Benedictine Abbey at Monte Cassino, an event that profoundly affected him.

Reportedly, Miller suffered from Post Traumatic Stress Disorder (PTSD) for 30 years before it was officially recognized and named. After the war, he converted to Catholicism, and in 1945, he married Anna Louise Becker. The couple had four children. In 1953, he briefly lived with science-fiction writer Judith Merril.