"Lord Brahma said: When the unlimitedly powerful Lord assumed the form of a boar as a pastime, just to lift the planet earth, which was drowned in the great ocean of the universe called the Garbhodaka, the first demon [Hiranyaksa] appeared, and the Lord pierced him with His tusk.
Purport: Since the beginning of creation, the demons and the demigods, or the Vaisnavas, are always the two classes of living beings to dominate the planets of the universes. Lord Brahma is the first demigod, and Hiranyaksa is the first demon in this universe. Only under certain conditions do the planets float as weightless balls in the air, and as soon as these conditions are disturbed, the planets may fall down in the Garbhodaka Ocean, which covers half the universe. The other half is the spherical dome within which the innumerable planetary systems exist. The floating of the planets in the weightless air is due to the inner constitution of the globes, and the modernized drilling of the earth to exploit oil from within is a sort of disturbance by the modern demons and can result in a greatly harmful reaction to the floating condition of the earth. A similar disturbance was created formerly by the demons headed by Hiranyaksa (the great exploiter of the gold rush), and the earth was detached from its weightless condition and fell down into the Garbhodaka Ocean. The Lord, as maintainer of the whole creation of the material world, therefore assumed the gigantic form of a boar with a proportionate snout and picked up the earth from within the water of Garbhodaka
When the Lord appeared to pick up the earth, the demon of the name Hiranyaksa tried to create a disturbance in the methodical functions of the Lord, and therefore he was killed by being pierced by the Lord's tusk. According to Srila Jiva Gosvami, the demon Hiranyaksa was killed by the hand of the Lord. Therefore his version is that after being killed by the hand of the Lord, the demon was pierced by the tusk. Srila Visvanatha Cakravarti Thakura confirms this version."
"Sri Vidura said: O chief amongst the great sages, I have heard by disciplic succession that Hiranyaksa, the original demon, was slain by the same form of sacrifices, the Personality of Godhead [Lord Boar].
Purport: As referred to previously, the boar incarnation was manifested in two millenniums--namely Svayambhuva and Caksusa. In both millenniums there was a boar incarnation of the Lord, but in the Svayambhuva millennium He lifted the earth from within the water of the universe, whereas in the Caksusa millennium He killed the first demon, Hiranyaksa. In the Svayambhuva millennium He assumed the color white, and in the Caksusa millennium He assumed the color red. Vidura had already heard about one of them, and he proposed to hear about the other. The two different boar incarnations described are the one Supreme Personality of Godhead."
"Materialistic demons sometimes appear to be very powerful and are seen to establish their supremacy throughout the world. Here also it appears that Hiranyaksa, by his demoniac strength, actually established his supremacy throughout the universe, and the demigods were afraid of his uncommon power. Not only were the demigods in space afraid of the demons Hiranyakasipu and Hiranyaksa, but so also were the aquatic animals within the sea.
Moving about in the ocean for many, many years, the mighty Hiranyaksa smote the gigantic wind-tossed waves again and again with his iron mace and reached Vibhavari, the capital of Varuna.
Vibhavari is the home of Varuna, lord of the aquatic creatures and guardian of the lower regions of the universe, where the demons generally reside. There Hiranyaksa fell at Varuna's feet like a lowborn man, and to make fun of him he said with a smile, "Give me battle, O Supreme Lord!"
Purport: Aggressive materialistic warriors are actually punished by the Supreme Lord for their policy of unnecessarily disturbing world peace. Therefore Varuna advised Hiranyaksa that the right course to satisfy his fighting spirit would be to seek to fight with Visnu.
Varuna continued: On reaching Him you will be rid of your pride at once and will lie down on the field of battle, surrounded by dogs, for eternal sleep. It is in order to exterminate wicked fellows like you and to show His grace to the virtuous that He assumes His various incarnations like Varaha.
Purport: Asuras do not know that their bodies consist of the five elements of material nature and that when they fall they become objects of pastimes for dogs and vultures. Varuna advised Hiranyaksa to meet Visnu in His boar incarnation so that his hankering for aggressive war would be satisfied and his powerful body would be vanquished.
Maitreya continued: The proud and falsely glorious Daitya paid little heed to the words of Varuna. O dear Vidura, he learned from Narada the whereabouts of the Supreme Personality of Godhead and hurriedly betook himself to the depths of the ocean.
He saw there the all-powerful Personality of Godhead in His boar incarnation, bearing the earth upward on the ends of His tusks and robbing him of his splendor with His reddish eyes. The demon laughed: Oh, an amphibious beast!
Purport: In a previous chapter we have discussed the incarnation of the Supreme Personality of Godhead as Varaha, the boar. While Varaha, with His tusks, engaged in uplifting the submerged earth from the depths of the waters, this great demon Hiranyaksa met Him and challenged Him, calling Him a beast. Demons cannot understand the incarnations of the Lord; they think that His incarnations as a fish or boar or tortoise are big beasts only. They misunderstand the body of the Supreme Personality of Godhead, even in His human form, and they deride His descent. In the Caitanya-sampradaya there is sometimes a demoniac misconception about the descent of Nityananda Prabhu. Nityananda Prabhu's body is spiritual, but demoniac persons consider the body of the Supreme Personality to be material, just like ours. Avajananti mam mudhah: persons who have no intelligence deride the transcendental form of the Lord as material.
The demon addressed the Lord: O best of the demigods, dressed in the form of a boar, just hear me. This earth is entrusted to us, the inhabitants of the lower regions, and You cannot take it from my presence and not be hurt by me.
You rascal, You have been nourished by our enemies to kill us, and You have killed some demons by remaining invisible. O fool, Your power is only mystic, so today I shall enliven my kinsmen by killing You.
The demon continued: When You fall dead with Your skull smashed by the mace hurled by my arms, the demigods and sages who offer You oblations and sacrifice in devotional service will also automatically cease to exist, like trees without roots.
Although the Lord was pained by the shaftlike abusive words of the demon, He bore the pain. But seeing that the earth on the ends of His tusks was frightened, He rose out of the water just as an elephant emerges with its female companion when assailed by an alligator.
The demon, who had golden hair on his head and fearful tusks, gave chase to the Lord while He was rising from the water, even as an alligator would chase an elephant. Roaring like thunder, he said: Are You not ashamed of running away before a challenging adversary? There is nothing reproachable for shameless creatures!
The Lord placed the earth within His sight on the surface of the water and transferred to her His own energy in the form of the ability to float on the water. While the enemy stood looking on, Brahma, the creator of the universe, extolled the Lord, and the other demigods rained flowers on Him."
Srimad-Bhagavatam, Excerpts 3:17:30-18:8
"Lord Boar very easily took the earth on His tusks and got it out of the water. Thus He appeared very splendid. Then, His anger glowing like the Sudarsana wheel, He immediately killed the demon [Hiranyaksa], although he tried to fight with the Lord.
Thereupon Lord Boar killed the demon within the water, just as a lion kills an elephant. The cheeks and tongue of the Lord became smeared with the blood of the demon, just as an elephant becomes reddish from digging in the purple earth."
Bhaktivedanta Book Trust. Excerpted from texts and purports of HDG A.C. Bhaktivedanta Swami Srila Prabhupada.