Goddess Rurujit is a fierce and unimaginably powerful form of Goddess Bhadrakali. Mother Goddess Kali took this form to defeat demon Ruru. This is mentioned in the Varaha Purana.
Legend has it that Goddess Roudri form of Mother Goddess Shakti was meditating on the foothills of Mount Neeli. During this period a powerful demon named Ruru wrecked havoc across the universe. He drove out the Devas or demigods from their abodes. The fleeing Devas approached Goddess Roudri.
Goddess Roudri could not bear her children being tormented. Her body became red hot and the universe was filled with a strange light that emanated from her. Embers appeared from her body and from the embers appeared Goddess Bhadrakali.
Goddess Bhadrakali ran towards Demon Ruru and engaged him in a fierce battle. Soon she overpowered the demon and killed him. As she killed demon Ruru, she came to be known as Rurujit.
Worship of Ruruji form of Goddess Kali is highly complex and powerful. Such temples are located mainly in Kerala.