Susannah Odetta Holmes Dean is the daughter of Alice and Dan Holmes, and a resident of New York City in 1964. She developed the split-personalities of Odetta Holmes (born 1941) and Detta Walker (born 1946) after Jack Mort dropped a brick on her head as a kid.
Roland Deschain accessed Holmes' mind through a door – marked "The Lady of Shadows" – on the shore of the Western Sea, and drew her into All-world. After her personalities were reconstituted into the individual of Susannah Odetta Holmes, Roland trained her as a gunslinger. She later married Eddie Dean, and helped Dean and Roland bring Jake Chambers into All-world by distracting a succubus.
As a result of her confrontation with the succubus, Susannah became pregnant, and eventually gave birth to Mordred Deschain in The Dixie Pig. She fought in the Battle of Calla Bryn Sturgis and the Battle of Algul Siento, and accompanied Roland all the way through the White Lands of Empathica into End-world, helping him to rescue Patrick Danville from the psychic vampire Dandelo. Ultimately, Danville conjured a door for her to pass through, and she was reunited with Dean, Chambers and Oy.