Prabhasa, one of the eight Vasus, stole, with support of bis brothers, Vasishtha’s wish-fulfilling cow. He cursed them for being born as humans on earth. The seven who weren’t really involved in the theft should go back to heaven immediately after they were born. Only the thief had to stay on earth.
Shantanu, the son of King Pratipa, met the river goddess Ganga while hunting, fell in love with her and married her. They had eight sons, seven of whom Ganga drowned immediately after giving birth. The eighth was Devavrata, whom she took with her when she left Shantanu. At the age of sixteen she brought him back to Shantanu, fully trained in state and martial arts. Shantanu had an heir to the throne in Devavrata.
Shantanu then fell in love with Satyavati, the daughter of a fisherman. The father was only willing to give her to Shantanu in marriage if her son became heir to the throne.
Devavrata vowed never to have a wife to ensure not to be the father of an heir to the throne. After this vow, Devavrata was called Bhishma, the one with the terrible vow.
Bhishma is the patriarch of the Kurus, often called the grandfather, Pitamaha, he raised the Kauravas and Pandavas and ruled in the background.
In 16 chapters the Mahabharata is told from Bharata to Pandu. The link is the first chapter. All chapters are found in June 2016.
A similar myth is Sadagarbha.