Masters of the Universe began as a line of toys in the 1980s featuring He-Man and other characters in a sword and sorcery setting. As the line was developed, a backstory was created in which He-Man and his allies fight to defend the supernatural secrets of Castle Grayskull from the evil forces of Skeletor. Following the success of these toys, Mattel sought to expand the female audience for the franchise. The Princess of Power toy line was introduced in 1985, featuring He-Man's sister She-Ra. By 1987, coinciding with the release of a live-action film, both Masters of the Universe and Princess of Power had faded in popularity, with the last of the Masters figures being released in 1988.