Peter Berresford Ellis is a British historian, literary biographer, and novelist who has published over 98 books to date either under his own name or his pseudonyms Peter Tremayne and Peter MacAlan. He has also published 100 short stories. Under Peter Tremayne, he is the author of the international bestselling Sister Fidelma historical mystery series. His work has appeared in 25 languages.

The historical mystery or historical whodunit is a subgenre of two literary genres, historical fiction and mystery fiction. These works are set in a time period considered historical from the author's perspective, and the central plot involves the solving of a mystery or crime. Though works combining these genres have existed since at least the early 20th century, many credit Ellis Peters's Cadfael Chronicles (1977–1994) for popularizing what would become known as the historical mystery. The increasing popularity and prevalence of this type of fiction in subsequent decades has spawned a distinct subgenre recognized by the publishing industry and libraries. Publishers Weekly noted in 2010 of the genre, "The past decade has seen an explosion in both quantity and quality. Never before have so many historical mysteries been published, by so many gifted writers, and covering such a wide range of times and places." Editor Keith Kahla concurs, "From a small group of writers with a very specialized audience, the historical mystery has become a critically acclaimed, award-winning genre with a toehold on the New York Times bestseller list."