Ma Katyayani is worshipped on the sixth day of Navratri. She is one of the most worshipped forms of Durga and is considered a destroyer of evil. She has four hands and she wields a long sword and a lotus in two of them. She blesses with the third hand and protects with the fourth one.
According to the legends, there was a sage known as ‘Kat’ who had a son named ‘Katya’. Later, a sage named ‘Katyayan’ took birth as his descendant. Sage Katyayan had no offspring. He observed austere penance and worshipped the gods for a child.
Meanwhile, the demon Mahishasura was creating a lot of trouble for the gods. His oppression was increasing day by day. The gods approached Vishnu to sought a way to end Mahishasura. At Vishnu’s behest, Shiva and Brahma joined him and then the Trinity (as Vishnu, Shiva and Brahma are collectively known as) emitted flames which took the form of Katyayani.
A manifestation of Durga, she then took birth as the daughter of Sage Katyayan as a result of which she came to be known as Katyayani.
Ma Katyayani was created to end the sins being committed by the demons and was born as a fighter. She had a resplendent form with three eyes, eighteen hands and was refulgent as a thousand suns. The gods gifted her with a lot of weapons to kill Mahishasura. Shiva gifted her a trident, Vishnu gave her a discus (Sudarshana Chakra), Varuna gave her a conch shell (shankha), Agni gave a dart, Vayu gave a bow, Surya gifted her a quiver, Indra gifted a thunderbolt, Kubera gave her a mace, Brahma gifted her a rosary and a water pot, Kala gave her a sword and a shield and Vishwakarma gave her a battle axe and many other weapons. Her vehicle is a lion.
Thus armed, Ma Katyayani proceeded towards Vindhya mountains where Mahishasura lived.
There is an interesting story on the birth of Mahishasura. His father Rambha, was the king of demons (asuras). He once fell in love with princess Mahishi, who was cursed to be a water buffalo. Mahisha is the Sanskrit word for buffalo. Mahishsura was born out of the union of Rambha and Mahishi. Due to his lineage, he was able to change form between an asura and buffalo.
A fierce battle took place between Ma Katyayani and Mahishasura. She defeated him and cut off his head with a sword. The slaying of Mahishasura is celebrated as Durga Puja in many parts of India. She is also named as Mahishasuramardini, the one who killed Mahishasura.
According to Bhagavata Purana, the young marriageable girls in Gokula observed fast during the entire month of Margashirsha and worshipped Goddess Katyayani to get Lord Krishna as their husband. They made an earthen deity of the goddess and worshipped it. From then on, it is believed, that girls who observe fast and worship Katyayani will find worthy husbands. In Tamil Nadu, Devi Kanya Kumari, the virgin goddess is said to be an avatar of Ma Katyayani. She is worshipped during the Pongal which also coincides with Makar Sankranthi.