Dattāteya is a Hindu deity considered to be an incarnation of Brahma, Vishnu, and Shiva, collectively known as Trimurti. The name Dattatreya is composed of two words - "Datta" (meaning given) and "Atreya", referring to the sage Atri, his physical father.
Various Hindu sects worship him differently, though Dattatreya is considered a form of all the three deities. He is especially considered an avatar of Vishnu while his siblings the moon-god Chandra and the sage Durvasa are regarded as forms of Brahma and Shiva respectively.However, In the Nath tradition, Dattatreya is recognized as an Avatar or incarnation of Shiva and as the Adi-Guru (First Teacher) of the Adinath Sampradaya of the Nathas. Dattatreya was at first a "Lord of Yoga" exhibiting distinctly Tantric traits,he is approached more as a benevolent god than as a teacher of the highest essence of Indian thought. However, spiritual seekers pray to this Supreme Teacher for knowledge of the Absolute Truth. Hinduist traditions credit Dattatreya as the author of the Tripura Rahasya given to Parashurama, a treatise on Advaita Vedanta. He is specially worshipped on his birthday, Datta Jayanti.
Shri Dattatreya, in order to bless His devotees, HE wanders in the form of a random guest in the afternoon. That is the reason a Guest has to be treated as the very embodiment of Lord Dattatreya.