Arunasura

In Hindu mythology, Arunasura was a demon, killed by Goddess Durga in the form of Bhramari Devi, who had attained the boon from Lord Brahma of not getting killed by any two- or four-legged creatures.

In the city of the demons, there lived a powerful demon named Arunasur. He was a furious God hater and a hypocrite.

With a view to conquer the Gods, he went to the banks of the Ganges in the Himalayas, practiced a very hard penance, to Brahma, taking him to be the protector of the demons. First influenced by Tamas Guna, he withheld in his body the five Vayus and partook only the dry leaves and repeated, the Gayatri Mantra and practiced austerities. Thus he practiced for full ten thousand years. Then for another ten thousand years the demon lived drinking some drops of water only; then for another ten thousand years he remained by inhaling air only; and then for another ten thousand years he did not take any thing and thus practiced his wonderful penance. Thus practicing his penance, a sort of wonderful halo of light emitted from his body and began to burn the whole world. The demon was practicing his austerities and saw that the demon was immersed in meditation with his eyes closed; and he looked, as it were, blazing with fire, as if a second fire himself. His belly had become dried up, body withered and the nerves of the bodies, too, became almost visible; only the life breath was lingering there.

Later, Arunasur had gotten the boon from Lord Brahma that he will not be killed by any two- or four-legged creatures. Then, puffed up with that boon, the demons Arunasur called on all the other demons that lived in the nether regions. The demons, that were under his shelter, came and saluted him, as their king and, by his command, they sent messengers to the Heavens to fight with the Gods. Hearing from the messenger that the demons were willing to fight with the Gods, Indra trembled with fear and went instantly with the Gods to the abode of Brahma.

Taking Brahma, too, along with them from there, they went to the Vaikunth and took Vishnu with them and all went to Kailash where Lord Shiva lived. There they all held a conference how to kill the demon, the enemy of the Gods.

While, on the other hand, Arunasur, the king of the demon surrounded by his army, went ere long to the Heavens. The demon, then, through the power of his penances, assumed various forms and seized the rights and possessions of the Moon, the Sun, Yamraj, Agni and all the others. All the Gods, then, dislodged from their stations went to the region of Kailash and represented to Lord Shiva about their own troubles and dangers respectively. They turned to Parvati, the part incarnate of the Supreme Goddess, to save them to kill Arunasur in the Himalayas, Parvati said that she will because she was aware of Arunasur's boon that he will be killed by six-legged creatures.

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Wikipedia