Once there were two demons named Shumbha and Nishumbha, who invaded devaloka and defeated the demigods.
Indra the ruler of the gods, along with the demigods went to the Himalayas to get Lord Shiva's help in retrieving their abode. Together, they prayed to Goddess Parvati (Durga).
Parvati heard their prayer while she was bathing, so she created another goddess, Chandi (Ambika) to assist the gods by vanquishing the demons.
Chanda and Munda were two demon generals sent by Shumbha and Nishumbha. When they came to battle her, Goddess Chandi created a dark goddess, Kali (in some accounts, called Kaalratri). Kali/Kaalratri killed them, thereby acquiring the name Chamunda.
Thereupon, a demon named Raktabija arrived. Raktabija had the boon that if any drop of blood of his fell onto the ground, a clone of him would be created. When Kaalratri attacked him, his spilt blood gave rise to several clones of him. As such, it became impossible to defeat him. So while battling, Kaalratri furious at this, drank his blood to prevent it from falling down, eventually killing Raktabija and helping goddess Chandi to kill his commanders, Shumbha and Nishumbha.
Another legend says that Goddess Chamunda (Kali) was the creator of Devi Kaalratri. Riding a powerful donkey, Kalraatri chased the demons Chanda and Munda and brought them to Kali after catching and incarcerating them. Then these demons were killed by goddess Chamunda.
Yet another legend recounts that, there was a demon named Durgasur who tried to attack Kailash, the abode of Parvati (Durga) in the absence of Shiva. Parvati got to know about this and created Kaalratri, instructing her to warn Durgasur against an attack. Durgasur's guards, however, tried to capture Kaalratri when she turned up as a messenger. Kaalratri then assumed a gigantic form and delivered the warning to him. Subsequently, when Durgasur came to invade Kailash, Parvati battled him and killed him gaining the name Durga. Here Kaalratri serves as an agent who gives the message and warning from Parvati to Durgasur.
The complexion of Kalaratri is that of the darkest of nights with bountiful hair and a heavenly shaped form. She has four hands - the left two hands hold a scimitar and a thunderbolt and the right two are in the varada (blessing) and abhaya (protecting) mudras. She wears a necklace that shines like the moon. Kaalratri has three eyes which emanate rays like lightning. Flames appear through her nostrils when she inhales or exhales.
Her mount is the donkey, sometimes considered as a corpse. Blue, red and white colours should be used to wear on this day.
The appearance of Goddess Kaalratri can be seen as bearing doom for evil-doers. But she always bears good fruits for her devotees and should avoid fear when faced with her, for she removes the darkness of worry from the life of such devotees. Her worship on the seventh day of Navratri is given especially high importance by Yogis and Sādhakas.
