Airavata was not human in shape; he was a large elephant. (See Sarga 14, Aranyakanda, Ramayana). KAURAVYA was a noble serpent which was born of Airavata. (M.B. Adi Parva, Chapter 218, Stanza 18).
Indra made Airavata his conveyance (vahana). There is a story of how Airavata was responsible for the churning of the milk-ocean (Ksirabdhi-mathanam). Once some maidens of devaloka presented a garland of flowers to sage Durvasas. When Durvasas visited Indra's court, he gave that garland to Indra. Indra put it on the tusks of his vahana, Airavata. The fragrance of the flowers attracted a swarm of bees which became an intolerable nuisance to Airavata. So Airavata tore the garland off his tusks and hurled it away. When Durvasas heard this, he took it as an insult. In his anger he cursed all the gods. The curse was that all gods should become subject to old age and the decrepitude and infirmities of old age. But though Durvasas cursed the gods, he also prescribed a remedy. The gods could redeem themselves from the curse by drinking Amrtam obtained from the ocean of Milk (Mahavisnu lies on the serpent, Sesa on this ocean). The curse began to operate and the gods lost their perennial youth. The gods then befriended the Asuras and with their help they churned the ocean of Milk. They got the nectar (Amrtam), drank it and regained their youth.
There is another story about Airavata. A story of how he also rose out of the ocean of Milk. It is said that when the devas and asuras churned the ocean of Milk, Airavata also came up along with the other good things. This story is narrated in the 18th Chapter of Adi Parva of the Mahabharata. The explanation given is that when Durvasas cursed the gods, Airavata was oppressed with a sense of guilt because he was responsible for the curse. So he took refuge in the ocean of Milk and there started propitiating Mahavisnu. There is however no warrant for such an explanation in the puranas. But the explanation sounds plausible because it explains the absence of Airavata during the interval between Durvasas's curse and the churning of the sea. Airavata is represented as a white elephant. It is probable that he became white after his long residence in the ocean of Milk. This lends some additional plausibility to the above explanation.
Airavata, the Lord of the elephants. In the Visnu Purana we are told how Airavata was made the chief of all elephants. When the Maharsis had crowned Prthu as the sovereign King, Brahma gave new posts of honour to many of the devas. He made SOMA (Moon) the lord of the Stars and Planets, of Brahmins, Yajnas and herbs. Kubera was made the overlord of all Kings; Varuna was made the master of the seas and all water; Visnu, the lord of the Adityas and Pavaka (Fire) the lord of the Vasus. Along with these Brahma made Airavata the lord of all elephants. (Chapter 22, Visnu Purana).
There is a story of how the tusks of Airavata were broken, narrated in the Asurakanda of Skanda Purana. Once an asura (demon) named Surapadma attacked devaloka. A fierce battle ensued between the gods and asuras. In the course of this battle, Jayanta, Indra's son, was hit by an arrow and at once he fell dead. Enraged by this Airavata rushed at Surapadma's chariot and shattered it to pieces. Airavata then attacked Surapadma who broke his tusks and hurled him down to the earth. Airavata lay paralysed for a long time; then he got up, retired to a forest and prayed to Lord Siva. With the grace of Siva, Airavata regained his lost tusks and was able to return to devaloka.
There is a belief that Airavata is one of the eight elephants guarding the eight zones of the universe. These eight elephants are called the Astadiggajas. Airavata is supposed to guard the eastern zone. (Chapter 66, Adi Parva, Mahabharata). Airavata and three other diggajas are supposed to reside in Puskara Island. (Chapter 12, Bhisma Parva, M.B.).
Indra's tusker Airavata was responsible for the churning of the ocean of Milk. But in the Mahabharata, Adi Parva, Chapter 18, Verse 42 it is said that a white elephant with four tusks arose during the churning of the ocean of Milk and that Devendra caught and tamed it. This is an obvious contradiction. Besides, in Valmlki Ramayana, Aranyakanda, 14th Sarga, the wounded Jatayu describing his family history to Sri Rama, gives the following account about the origin of Airavata :
Kasyapa, one of the Prajapatis, married the eight daughters of Daksa. One of them named Krodhavasa had ten daughters by Kasyapa. They were: Mrgi, Mrgamada, Hari, Bhadramada., Mataiigl, Sarduh, Sveta, Surabhi, Surasa and Kadru. Of them Bhadramada gave birth to a daughter, Iravati. The tusker Airavata is Iravati's son.
An explanation for this discrepancy may be seen in Visnu Purana, 3rd Section, Chapter 1. Now six Manvantaras have passed. This is the seventh Manvantara. Each Manvantara has a new Indra. According to this, different Indras have their own Airavatas. This is the only explanation for this apparent contradiction.