Who is Kali, and what is she known for?
Kali is a complex Hindu goddess. She is sometimes identified as the wife of Shiva, Durga (“The unattainable”) but in an even more frightening form than even she. Whereas Parvati, the Earth Goddess, is nurturing, Durga/Kali is the opposite. She is death and destruction, but, to some she is the instrument of rebirth too. In Tantric Hinduism, she came to be the Supreme divinity. Kali was the goddess associated with the famous thugee (from which English gets the word thug), a secret society that would ambush British travellers, and kill by strangulation. Wikipedia has an excellent article, in which it mentions that Kali appears in the Rig-Veda, but as one of the seven tongues of Agni, the fire.
