When Siva learned of his wife Sati’s self-immolation in the sacrificial fire of her father Daksha, he loosened his matted hair in full anger. Out of this angry energy were born two attendants: Veerabhadra and Bhadrakali. Bhadrakali was the angry energy of Parvati in a feminine form. Siva sent them to kill Daksha.
This part of the Siva myth cycle involves the killing of a brahmin. Even Siva could not do that directly. Devotees of Lord Vishnu used this myth to argue that SSiva was not invited to Daksha’s Vedic sacrifice because of his impurity and that his killing of a brahmin, even indirectly, by sending his creations, made him guilty of the greatest sin against dharma (duty, righteousness).
In a later myth Bhadrakali made a dramatic appearance in the Krishna birth story. In order for Krishna to escape death at his birth at the hands of his evil uncle Kamsa, a baby girl was substituted. As Kamsa tried to kill her, Bhadrakali appeared in full glory and power.
She also played a role in the Rama-Ravana war. Parvati complained to Siva that she had not been given a role in Vishnu’s Rama incarnation. So Siva caused her to lose consciousness of her true nature and be reborn as Lanka-Lakshmi, a doorkeeper or guardian in Lanka for Ravana. She fought with Hanuman, who knocked her unconscious with a blow from his left hand. When she regained consciousness, she remembered that she was Bhadrakali. She thanked Hanuman and returned to Kailash and SHiva.