Destroyer of evil, Maa Katyayani, she was created out of spontaneous anger of the gods which eventually led to the killing of the demon, Mahishasur. Riding a lion, depicted with four arms, Maa Katyayani is worshipped on the sixth day of Navratri.
As one of the most worshipped avatars of Maa Durga, She was born to a Rishi named Katyayan, hence the name Katyayani. When a demon named Mahishasur was creating havoc, the gods approached Lord Vishnu for help. Lord Vishnu along with Lord Brahma and Lord Shiva came together and with their combined powers manifested Maa Katyayani.
Maa Katyayani has three eyes, and rides a ferocious lion. In her four hands, she carries a lotus and a sword in left hands each and one right hand in Abhayamudra (blessing hand posture) and other in Varadamudra (posture dispensing boons) postures. A fierce battle ensued between Maa Katyayani and Mahishasur demon, who could change form into a demon and a buffalo at will. Maa Katyayani slays Mahishasur with Her sword, because of which She is also known as Mahishasurmardini. This is celebrated in many parts of India as Durga Puja.
Each day of the Navratri is devoted to one of the nine avatars of Maa Durga. The nine different forms are Shailaputri, Brahmacharini, Chandraghanta, Kushmanda, Skandamata, Katyayini, Kaalratri, Mahagauri and Siddhidhatri.