This is considered as 3rd avatar among the 10 avatars of Lord Vishnu. This is a Big avatar (Viswathma) represented by the sound Viswam in Vishnu Sahasranamam. The reference to this avatar is mentioned as Maha Varaha Govinda. The universe which the Lord measured with his giant stride is sitting as a small bundle on the tip of the nose of Varaha.
Let us see how this came about. As Brahma sat ruminating as to how to carry on the work of creation when the earth is submerged in water. At that time a tiny boar jumped out of his nostril as big as the upper part of the thumb. It started growing until it reached the size of a mountain rock and roared loud. The Boar went about smelling to discover Mother Earth lying submerged in water. The skin of the Boar represented Vedic Mantras, bristles – Kusa grass, belly the plate and the snoot a wooden ladle. When he was lifting the earth upwards on the end of his tusks, Hiranyaksha challenged him. He then placed the Earth on the surface of the water and the proceeded to meet the challenge of Hiranyaksha who ridiculed the Lord for running away. A wordy duel followed and at the end of its Hiranyaksha sprang upon the Lord and dealt him with a blow with his mace. Hiranyaksha or Hiryaksha and the Lord went on attacking each other, Brahma who came with thousands of sages and seers spoke to the Lord thus: the hour of Abhijit (Auspicious period) has passed and therefore slay him and bring peace to the world. After a fierce battle, the Lord slapped him in the root of his ear and the demon fell dead.
Having thus killed Hiranyaksha, Lord Narayana who had taken the avatar of a Boar retired to his own divine realm.