The Demon God
The incident happens thousands of years ago when Gods in Heaven got arrogant. They started going against their duties, given to them by the Omnipotent God-Almighty, the supreme being who has no form or size and completely invisible but exists everywhere. Then to bring them out from that illusion, HE (the omnipotent God-Almighty) made the demon God and gave boon to him that he will not be killed by any God (the deities). HE also granted him many unlimited powers to fight war against Gods in Heaven.
The powers of the Demon God
As the omnipotent God Almighty has given him many unlimited powers, so the powers of the Demon God are unlimited. He has many evil powers which can never be defeated by any God in Heaven. Even the trinity (Tridev) cannot defeat or kill him. He is beyond their powers.
Action by the Demon God
The action by the Demon God was very well planned and terrible. As he, himself, was a God of demons, he beget many demons and other evil powers. Those demons did austerity of the Gods in Heaven, got boons from them and after becoming powerful, they invaded on Heaven. The demons were so powerful that they defeated all Gods in the Heaven including their King named Indra and put them jailed in the Hell.
Gods begged for forgiveness
When all Gods of Heaven were jailed in the Hell by the Demons, they (deities) felt sorry for their deeds which they did in arrogance. Then Gods begged for forgiveness from the omnipotent God Almighty.
The Demon God became arrogant
Up to then around 500 years passed. After getting so many unlimited evil powers and all Gods of heaven in the prison, now the demon God became arrogant and went against the wishes and orders of the Omnipotent-God-Almighty. He became very cruel to the Gods of heaven and planned to capture the World of Humans also. Now he wanted to rule over the Universe including humans.
Creation of an extra ordinary human being to kill the demon God
As nobody was there in the entire universe who can stop or kill the demon God, so keeping all the situations in view, the Omnipotent God Almighty made an extra ordinary human being to kill the demon God. That human being was a sage, simple, loving to all and powerful than all Gods.
The Gods of Heaven were freed
By the creation, wish and inspiration of the omnipotent God Almigty, the incarnation of that human sage came in existance. He did so terrible austerity that it started dreadful fire coming from him. The flames of that fire were going higher in the sky destroying everything around and far away. It was becoming more and more powerful. The powers of that human sage were beyond the powers of the demon God.
When the demon God saw the power of that human sage, the Gods of Heaven were freed from the Hell by him and thus the deities took their charges of duty towards the creation again. They started bringing up the creation using their powers from heaven. By this way, everything was good in the heaven now.