Dhoomravarna is Ganesha's eight incarnation. Ahantasura,
the demon of pride, had learnt the Ganesha mantra from the demon priest,
Shukracharya. He chanted the mantra for a thousand years and Ganesha
blessed him with the boon of being invincible. Ahantasura began spreading
terror everywhere. The gods went to Shiva and Vishnu and were asked to
chant the Ganesha mantra.
Ganesha finally appeared as Dhoomravarna after a thousand years of
prayers. He sent Narada to Ahantasura advising him to give up all his
wrong deeds, but the demon did not agree. Angry at the demon's behaviour,
Dhoomravarna threw his Ugrapash, the noose, and destroyed his entire army.
Ahantasura ran to Shukracharya for help, who advised him to surrender.
Ahantasura fell at Dhoomravarna's feet and prayed for forgiveness. Though
he was forgiven, Ahantasura was restricted to staying only in patal lok