Worship of God as Mother has been in vogue in India since the most ancient times. Out of the several aspects of the Mother Goddess that are still worshipped, an overwhelming majority are forms of Pārvatī or Śakti, the consort of Śiva. Bhadrakālī is one of them.
Since ‘bhadra’ means auspiciousness, Bhadrakālī is a pleasing deity with a charming appearance. She is depicted as seated on a chariot drawn by four lions. She has eighteen hands in which she carries things such as rosary, trident, sword, shield, bow and arrow, conch, discus, sacrificial ladles, holy water-pot, spear and so on. One of the hands is raised in the gesture of benediction.
The girl-child of Yaśodā which was brought to the prison by Vasudeva, the father of Kṛṣṇa, after exchanging it with baby Kṛṣṇa, and which Kaṁsa tried to kill, was also Bhadrakālī. She is an aspect of Durgā.
The Kālikāpurāṇa (ch. 59) however describes Bhadrakālī as an aspect of Durgā, and as an exceedingly terrible deity. The demon Mahiṣāsura saw her in dream and was stricken with mortal fear. He worshipped her and got the boon to be killed directly by her. She also granted an additional boon that he too would be worshipped in future along with her.
According to another account Bhadra-kālī was the female companion of Vīra-bhadra, who had been created by Śiva out of a hair from his matted locks to destroy Dakṣa’s sacrifice.