Lord Dattatreya is the incarnation of Brahma, Vishnu and Shiva.
Sage Narada praised Anusuya's "pativratyam" (Devotion to her husband) a lot before the wives of Brahma-Vishnu-Shiva making them jealous of her. They requested their husbands to reduce her pativratyam. Brahma, Vishnu and Shiva went to Anusuya as guests when Atri was not there at home and asked her to serve them food. When she agreed to do so, they said that they will accept her alms on the condition that she serves them without wearing clothes. Anasuya falls into a dilemma.
If she comes without clothes in front of other men her pativratyam will be reduced. If she refuses then that is dishonor to the guests and they can take away all the power of Atri. Anasuya felt that the three guests who asked such a strange favor are not normal people since they are trying to place her in a tricky situation.
Anasuya prayed to her husband in her mind and said that she doesn't have any fear serving them without clothes as she is not affected by lust. Since the guests asked for alms saying "Bhavati Bhiksham Dehi" (Oh Mother! Give us some food) and indirectly called her a mother. She decided that she will consider them as her children and serve them as requested. Because of her greatness and as per her thinking by the time she came to serve food the three gods became small children and her breasts started producing milk. She then breastfed them and put them to sleep in a cradle. Atri came back afterwards and hearing the story from Anasusuya praised the three gods sleeping in the cradle. They woke up in their original form and praised Anasuya's pativratyam and gave her a boon. Anasuya requested that these three should be born as her children—the incarnation of Shiva, Vishnu and Brahma as sage Durvasa, Dattareya and the moon-god Chandra.
Dattatreya left home at an early age to wander naked in search of the Absolute. He seems to have spent most of his life wandering in the area between and including North Karnataka, through Maharashtra and Andhra Pradesh, and into Gujarat as far as the Narmada River. He attained realization at a town, now known as, Ganagapura in North Karnataka. The original footprints of Datta are believed to be located on the lonely peak at Girnar. The Tripura-rahasya refers to the disciple Parashurama finding Datta meditating on Gandhamadana mountain.
According to Brahma Purana, after an order from his father, Sage Atri, Dattatreya sat on the banks of river Gautami and prayed to Shiva and finally earned the Brahmagyaan (Eternal Knowledge). This is possibly the reason why Dattatreya is considered as Adisiddha in Nath Sampradaya. In the Uddhava Gita a song embedded in the Bhagavata Purana, there is a story of Dattatreya sung by Krishna which enumerates a list of his twenty-four gurus: earth, air, sky or ether, water, fire, sun, moon, python, pigeons, sea, moth, bee, bull elephant, bear, deer, fish, osprey, a child, a maiden, a courtesan, a blacksmith, serpent, spider, and wasp. The 24 Gurus of Dattateya come from the 24 gurus of Avadhut described in the Purana.
The disciples of Dattatreya are: Kartavirya Arjuna, Parashurama, Yadu, Alarka, Ayu and Prahlad. These are known from Puranas. There is one more by name Sankruti described in Avadhutopanishad and Jaabaaldarshanopanishad.
As an avatar
In The Pathless Path to Immortality, Mahendranath writes: Shri Dattatreya was a dropout of an earlier age than the period when Veda and Tantra merged to become one simple cult. It was men like Dattatreya who helped to make this possible. Three of his close disciples were kings, one an Asura and the other two both belonging to the warrior caste. Dattatreya himself was regarded as an avatar of Maheshwara (Shiva) but later was claimed by Vaishnavites as the avatar of Vishnu. Not such a sectarian claim as it appears; Hindus regard Shiva and Vishnu as the same or as manifestations of the Absolute taking form.[unreliable source?] Indeed, the Dattatreya Upanisad, which opens proclaiming Dattatreya's identity with Vishnu, ends with the mantra Om Namah Shivaya, identifying Datta with Shiva. In the last portion of the third chapter, Mahesvara (Shiva) alone is said to pervade reality and shine in every heart of man. He alone is in front, behind, to the left, to the right, below, above, everywhere the center. Finally, Mahesvara is identified with Dattatreya, depicting the latter as an Avatara of Shiva.
The nectar of the honey-bee
Rigopoulos (1998: p.xii) conveys the motif of the '"honey bee" Yogin' (as an aside, the literary point of origin of this motif may be the Nad-Bindu Upanishad of the Rig Veda) common to nondual Dharmic Traditions and champions Dattatreya as the archetypal model of inclusionism and syncretism by implication: Furthermore, the unfolding of the Dattātreya icon illustrates the development of Yoga as a synthetic and inclusive body of ideologies and practices. Although fundamentally a jñāna-mūrti, Dattātreya is a "honey bee" Yogin: one whose character and teachings are developed by gathering varieties of Yoga's flowers. For all religious groups whose propensity it is to include ideas, practices, and teaching from the ocean of traditions, Dattātreya is truly a paradigm.
Dattatreya is usually depicted with three heads, symbolizing Brahma, Vishnu, and Shiva; past, present and future; creation, preservation and destruction; aPre-Vedic Indian dogs were regarded as auspicious symbols, and later deities assumed dog forms, became associated with dogs, and were linked with the glory and fidelity of warriors. Four different-coloured dogs accompanied the Dattatreya, who represented the four Vedas... Dogs also held the cultural significance of 'dog eaters' (Sanskrit: candala) those who existed beyond the confines of Varnashrama Dharma. Dogs are also both wild, tame and symbols of fidelity and devotion (Sanskrit: bhakti).
Dattatreya is one of the oldest deities. The first reference of this deity is found in epics like Mahabharata and Ramayana. In the Dattatreya Upanishad which is a part of the Atharva Veda, he is described as being able to appear in the form of a child, madman, or demon in order to help his devotees achieve moksha, liberation from the bonds of worldly existence. The single head for Dattatreya can be explained if one sees the Tantric traditions which prevailed in India about 1000 years back. It was Gorakshanath who changed removed the aghori traditions and made the Nath sampradaya in the acceptable civil form of today. Dattatreya must have been a very powerful sage existing before this time and over the centuries sometime he was defined to the form of Dattatreya. The three heads have come definitely later in the last 900 years or so.nd the three states of consciousness: waking, dreaming and dreamless sleep. He is portrayed sitting in meditation with his shakti beneath the 'wish tree' (Sanskrit: Kalpavriksha) with the 'wish cow' (Sanskrit: Kamadhenu) attendant. In front of him is a 'fire pit' (Sanskrit: Agnihotra) or 'pit' (Sanskrit: homa) the receiver of the oblation of 'sacrifice' (Sanskrit: yajna), and around him are four dogs.
Werness (2004: p. 138) ventures the semiology of the four dogs each of a different colour oft-depicted in Dattatreya iconography as holding the valence of the four Vedas: