Peter Berresford Ellis (born 10 March 1943) is a historian, literary biographer, and novelist who has published over 90 books to date either under his own name or his pseudonyms Peter Tremayne and Peter MacAlan. He has also published 95 short stories. His non-fiction books, articles and academic papers have made him acknowledged as an authority on Celtic history and culture. Under Peter Tremayne, he is the author of the international bestselling Sister Fidelma mystery series. His work has appeared in 25 languages.