Ambalika was the daughter of King of Kashi and the wife of Vichitravirya, King of Hastinapur.
Along with her sisters Amba and Ambika, she was taken by force by Bhishma from their Swayamvara. (Bhishma challenged the assembled kings and princes and defeated them.) He presented them to Satyavati for marriage to Vichitravirya.
After Vichitravirya's death, his mother Satyavati sent for her first born, Rishi Veda Vyasa. According to his mother's wishes, he visited both the wives of Vichitravirya to grant them a son. Ambalika was instructed by Satyavati to keep her eyes open lest she would bear a blind son like Ambika (Dhritarashtra). She did keep her eyes open but she became pale after seeing the formidable form of the Sage. Hence her son, Pandu the father of the Pandavas, was born sickly.