About Vritrasura:
http://www.sarathi.co.uk/srimad_bhagavat_katha_day4_2.htmNaradji then appeared and rather than giving Daksha a curse in return he advised daksha that he should create Daughter rather than sons. Daksha created sixty daughter. Ten weded dharma, thirteen to Kashyap muni, twenty seven to Chandra, two to Angira , two to Tarksh, two to krushaswa and two to Bhuta deva.
Out of the thirteen that are weded to Kashyap, one is called Ditti and one is called Aditti. All the sons of Ditti became demonic and all the sons of Aditti became devine. Aditti had twelve sons and the eldest was Vivaswaan also know as sun.son number two is Aryaman, third is Pusha and fourth twatsta. Twatsta has two sons. Samvinesh and Vishvaroop. All the devta made Vishvaroop a Guru and then Killed him. Bhrhaspati left the deva and so the deva made Vishvaroop a guru.
One day indra invited all the deva and some dancer to perform. When the dancer were performing , Indra and all deva were so engrossed that when Bhrhaspati, their guru, was arriving they continued to observe the dance and did not pay their respect to the Guru. Bhrhaspati went back to the Ashram, said to his wife Taramati, from today I am no lobger the Guru of the devas. I am going on meditation and should some one ask for me then let them that I am meditaion but not sure where.
The devas were all still very much involved in the dancing. For self enjoyment.
There are two form of dancing, one for self enjoyment and the other for the Lord.
Sukracharya realised that the devas no longer have a guru and to asked all the Asura to attack the heaven as it is now weak. The asura took over the heaven and the devas went to Brahma for advised. Brahma advised that Vishvaroop would make a good Guru.
All the devas went to see Vishvaroop and said that we have come you as guest and need you to be our Guru. Vishvaroop replied, "you did not look after your Guru, how can I be sure that you will look after me?"
The devas started pleading so Vishvaroop agreed. First Vishvaroop gave Indra the knowledge of Narayan Kavach. Armed with this Indra attacked the Asura and reclaimed the heaven. After reclaiming the heaven Indra performed a yagna.and drank Somrup. Vishvaroop gave some somrus to the Asura because to him the asura and devas are equall, and that created conflict with Vishvaroop and devas and Indra Killed Vishvaroop. Vishvaroop's Father Twatsta became very angry and performed a Yagno to created an enemy of indra to kill indra.
However performing pooja in anger leads to mistakes and and that can mean a heavy price. Twatata , instead of asking for a son who can kill Indra he asked for a son who would be kill be Indra. A large figure came out of the yagna called Vritrasur.Twatsta asked Vritrasur to go and kill Indra. Sucrachrya asked all the asura to help Vritrasur and once again a great war took place. The deva are very powerfull and death of vritrasur is certain.Vitrasura still fought well. The fight went on and it soon became dark. Vtritrasur destroyed all the devas weapons and the devas ran to brahma.Brahma advised that they should go and make a weapon from bones of Dadhichi rushi. Indra went to Dadhichi rushi and for his bones .
Dadhichi said that to give up ones body for the sake of the society is an act of seva. Dadhichi took samathi and surrender his bones to Indra. Then Indra went back into battle armed with this divine weapon. Indra was going to kill Vrutrasur. Just then he request that he want to do s Stuti to the Lord before his death. In the stusti Vritrasur asked the Lord that is waiting to become the servant of his servant. Vristrasur then died at the hands of Lord Indra.
Vritrasur was a son of a Brahman so after killing Vritrasusr Indra went to mansaravar and hid in the lake to punish himself. Indra wives went to Bhrhaspati and asked for forgiveness and become the Guru of the Devas again. And lso releave Indra from his bad deed of killing a Brahman. Brhaspati agreed and indra was soon back in heavens.