Wikipedia
In Hindu mythology, Kalmashapada (Kalmasapada, कल्माषपाद), also known as Saudasa , Mitrasaha , Amitrasaha and Kalmashanghri (Kalmasanghri), was a king of the Ikshvaku dynasty (the Solar dynasty), who was cursed to be a rakshasa (demon) by the sage Vashishtha. He is described as an ancestor of Rama, the avatar of the god Vishnu and the hero of the Hindu epic Ramayana. Many texts narrate how Kalmashapada was cursed to die if he had intercourse with his queen, so he obtained a son from Vashishtha by niyoga, an ancient tradition whereby a husband can nominate another man to impregnate his wife. Kalmashapada's story is narrated in various works including the classic epic poems Mahabharata and Ramayana, and the Puranas.