Since the beginning of the universe the TRIDEV created the astras for the safety of humanity. out of these, 3 are known as MAHASTRA - BRAHMASTRA, NARAYANASTRA and PASHUPATASTRA. when these 3 combine they create the powerful BRAHMASHIRASTRA.
To bring BRAHMASHIRASTRA on earth we need to gather the three orbs of Brahma, Vishnu and Shiva in a triangle formation which contain the power of the 3 mahastra . To protect these orbs the last avatar of God gave these orbs to a secret group of people known as ASTRADHARI. then GOD descended back to heaven and Kaliyug began . with the rise of Kaliyug the demons got stronger within them was one who wanted to get hold of the BRAHMASHIRASTRA. He worshipped the Creator(Brahma) for years and got 2 boons then he began destruction of empires.