Mercedes Ritchie Lackey is an American writer of fantasy novels, born on June 24, 1950. Many of her novels and trilogies are interlinked and set in the world of Velgarth, primarily in and around the country of Valdemar. Her Valdemar novels feature interactions between human and non-human protagonists across various cultures and social mores.

Her other primary fictional world is akin to Earth but features hidden populations of elves, mages, vampires, and other mythical beings. The Bedlam's Bard books, for example, tell the story of a young man capable of performing magic through music; the SERRAted Edge series features elves who race cars; and the Diana Tregarde thrillers focus on a Wiccan heroine battling evil.

Lackey has also published several novels that reimagine well-known fairy tales, set in a magical yet hidden world resembling the mid-19th to early 20th century. These works explore themes such as ecology, social class, and gender roles. Lackey has published over 140 books, maintaining an impressive rate of approximately 5.5 novels per year. In 2021, she was honored as the 38th Damon Knight Grand Master. She has been recognized as one of the "most prolific science fiction and fantasy writers of all time."