According to Apollodorus he married Asia, the daughter of his brother Oceanus, and became by her the father of Atlas, Prometheus, Epimetheus, and Menoetius, who was slain by Zeus in the war against the Titans, and shut up in Tartarus.
Hyginus, who confounds the Titans and Gigantes, makes Japetus a Giant, and calls him a son of Tartarus.
According to Homer Japetus is imprisoned with Cronus in Tartarus, and Silius Italicus relates that he is buried under the Island of Inarime. Being the father of Prometheus, he was regarded by the Greeks as the ancestor of the human race.
His descendants, Prometheus, Atlas, and others, are often designated by the patronymic forms Japetidae (es), Japetionidae (es), and the feminine Japetionis.
Another mythical personage of the same name, the father of
Buphagus, is mentioned by Pausanias.