Dadhichi was a great Sage who was born to Atharva. He was an ardent devotee of Lord Shiva and known for his great sacrifice.
He did severe penance for years together and had acquired great powers. His penance had terrified Lord Indra, who was afraid that Dadichi might capture heaven from him. But Dadichi was not interested in all that and continued his devotion to God.
Later a Brahmin by name Vrutrasura became the head of demons and was troubling the devas. Vrutrasura had become so powerful that the Gods did not know what to do with him and approached Lord Vishnu seeking his help.
Vishnu declared that only a weapon made from the bones of a pious rishi can help to kill Vrutrasura. The Gods did not know of anyone who would be ready to part with their bones . But Vishnu advised them to go to Sage Dadhichi who would help them in this task.
When Dadhichi was informed about this, he did not even think for a moment and decided to donate his bones to the cause. Dadhichi became lifeless in as short while and Lord Indra made the VajraAyudha from his bones.
The devas went on to win the war against demon Vrutrasur with the weapon made of Dadhichi’s bones. This way the sacrifice of the great Sage Dadhichi saved the Gods from the demons.