On one particular occasion, Shiva addressed Parvati as “Kali.” The word kali means dark and Parvati thought that Shiva referring to her dark complexion. She did not realize that Shiva was merely trying to tease her a bit. Greatly incensed at the imagined slight, Parvarti decided that she would meditate so that she might become fair. She wore clothing made of barks of trees and performed tapasya. In the summer she prayed inside a raging fire and in the winter she prayed under the water. Sometimes, she ate only roots and fruits. At other times, she fasted. Prior to leaving for her tapasaya, Parvati had instructed Nandi that he was to stand guard at Shiva’s door and permit no other woman to enter.
There was a demon named Adi. This fellow had performed a lot of tapasya and had manage to please Brahma. When Brahma agreed to grant him a boon. Adi asked for the boon of immortality. Brahma naturally refused this boon. He however granted Adi the boon that the demon would die only when he changd his form twice, not otherwise. Adi happened to come to Shiva and Parvati’s house and discovered Nandi standing guard at the door.
Wondering what there was to be guarded, he adopted the form of a snake and slithered in. Nandi did not notice the snake, but this was Adi’s first transformation. Inside the house, Adi encountered Shiva and thought that he would play a trick on Shiva. He adopted Parvati’s form. This was his second transformation. In the form of Parvati, Adi went up to Shiva and greeted him. Initially, Shiva did not realize that this was not Parvati. He greeted the demon and said, “Darling, I am delighted that you have returned. I can see that your rage has cooled down.” But in a little while Shiva realized that this was not Parvati. He slew the demon. Meanwhile, Parvati was continuing with her tapsaya and pleased Brahma with her prayers. Brahma granted her the boon that she would become fair. Since the word gouri means fair, Parvati was thereafter known as Gouri. A goddess named Koushiki emerged out of Parvati’s cells, thus named because the word kosha means cell.
The darkness of Parvti’s complexion entered Koushiki’s body. Brahma requested the goddess Koushiki to go and live in the Vindhya mountains. She is therefore also known as Vindhyavasini.