In the Mahabharata, Bhishma was the son of Shantanu and Ganga . Birth of Bhishma and his suffering on earth is due to a curse in his previous birth. Ganga before marrying Shantanu had taken word from him that he will not question any of her actions.
Ganga soon gave birth to Shantanu’s first child. Immediately, Ganga took the child to river and drowned it.
Shantanu said nothing. She gave birth six more times and Ganga performed the horrific deed six times.
When the eighth child was born, Shantanu questioned Ganga ’s merciless behavior. Ganga then told that Shantanu had broken his promise and she will leave him and return to heaven.
She also told Shantanu that the children that she killed were seven of eight Devas known as Vasus. They had once stolen the cow of Sage Vasishta and were cursed to be born as humans.
To save them from suffering, Ganga became their mother and spared them from suffering on earth by killing them as soon as they were born.
The eighth Vasu is destined to suffer and will live a long life. This was Bhishma.