Kali is a form of Durga that sprang from her head during Durga's battle with the demon Raktabija (who represents the power of thoughts, the power which constantly and unceasingly reproduce in the mind) whose blood when touch to the earth generated another Raktabija. To end this battle between Raktabeeja and Durga, Kali consumed every drop of blood until Raktabija Bled out. 