The Story of Mahishasur

Mahishasura the demon was born as a union of Rambha and a she buffalo (Mahishi) and consequently was a half man and half buffalo. The mighty demon was rendered more powerful as a result of a boon from God Agni, according to which he could be killed by a woman only. He managed to wreak havoc in heaven by chasing away all Gods from there. All the Gods then approached lord Vishnu and lord Shiva who were aware that only a woman could kill Mahishasura. They decided to create a Goddess out of the collective powers or 'Tejas' of all the God's and so was born a Goddess who combined in herself all that was mighty and powerful in each God. She was armed by a trident from Shiva, Chakra from Vishnu, a Lion from Himalayas and bows and arrows from Vayu. The Goddess filled with combined power and anger of all the Gods was fierce to behold and her very sight scared the demons. 

Mahishasura on the other hand, waged a valiant fight against her and assumed the form of a buffalo, a lion, a man carrying a sword, an elephant and lastly again as a buffalo. The battle raged for ten thousand years and finally the Goddess was able to pin down Mahishasura and chop off his head. The Gods, rid of the demon, showered the Goddess with innumerable praises and with reverence prayed her to appear every time they were in need of her. Granting the same to the Gods, she disappeared to appear again when called with devotion.