Yagya or Yajna or Yagneshwara("Lord of yagya") is mentioned as an Avatar

Avatar

In Hinduism, an avatar is a deliberate descent of a deity to earth, or a descent of the Supreme Being and is mostly translated into English as "incarnation," but more accurately as "appearance" or "manifestation"....

 of the Hindu god Vishnu

Vishnu

Vishnu is the Supreme god in the Vaishnavite tradition of Hinduism. Smarta followers of Adi Shankara, among others, venerate Vishnu as one of the five primary forms of God....

 in Bhagavata Purana

Bhagavata purana

The Bhāgavata Purāṇa is one of the "Maha" Puranic texts of Hindu literature, with its primary focus on bhakti to the incarnations of Vishnu, particularly Krishna...

. As Yagya, Vishnu is the embodiment of the Hindu fire sacrifice ritual or yagya. He was also the Indra

Indra

' or is the King of the demi-gods or Devas and Lord of Heaven or Svargaloka in Hindu mythology. He is also the God of War, Storms, and Rainfall.Indra is one of the chief deities in the Rigveda...

 of the Svayambhuva Manvantara, era of Svayambhuva Manu.

Mythology

The Bhagavata Purana, Devi Bhagavata Purana, and Garuda Purana

Garuda Purana

Garuda Purana is one of the Puranas which are part of the Hindu body of texts known as smriti. It is a Vaishnava Purana and its first part contains a dialog between Vishnu and Garuda, the King of Birds...

 list Yagya or Syavambhuva as an avatar of Vishnu or Adi-Narayana

Narayana

Narayana or Narayan or Naraina is an important Sanskrit name for Vishnu, and in many contemporary vernaculars a common Indian name. Narayana is also identified as the original man, Purusha. The Puranas present divergent views on Narayana...

. Yagya is classified as a one of the 14 main Manvantara-avatars (an avatar corresponding to a Manvantara and who supports the corresponding Indra and other gods to maintain the principles of religion) called vaibhava-avatars. Yagya is also categorized as a Kalpa-avatar (an avatar corresponding to an aeon called Kalpa) of Vishnu.

Yagya is the son of Prajapati

Prajapati

In Hinduism, Prajapati "lord of creatures" is a Hindu deity presiding over procreation, and protector of life. He appears as a creator deity or supreme God Viswakarma Vedic deities in RV 10 and in Brahmana literature...

 Ruci and Akuti, the daughter of Svayambhuva Manu - the first Manu (progenitor of mankind). During the period of Svayambhuva Manu (Svayambhuva Manvantara), there was no qualified Indra

Indra

' or is the King of the demi-gods or Devas and Lord of Heaven or Svargaloka in Hindu mythology. He is also the God of War, Storms, and Rainfall.Indra is one of the chief deities in the Rigveda...

, the post of the king of Svarga

Svarga

In Hinduism, Svarga is a set of heavenly worlds located on and above Mt. Meru. It is a heaven where the righteous live in a paradise before their next reincarnation...

 (Heaven) and king of gods. So, Vishnu incarnated as Yagya and held the post of Indra.

Vishnu Purana

Vishnu Purana

The Vishnu Purana is a religious Hindu text and one of the eighteen Mahapuranas. It is considered one of the most important Puranas and has been given the name Puranaratna...

 tells that Yagya had a twin sister named Dakshina ("donation"). Later, Yagya married Dakshina and had twelve sons. These twelve Devas

Deva (Hinduism)

' is the Sanskrit word for god or deity, its related feminine term is devi. In modern Hinduism, it can be loosely interpreted as any benevolent supernatural beings. The devs in Hinduism, also called Suras, are often juxtaposed to the Asuras, their half brothers. Devs are also the maintainers of...

 (gods) are collectively called the Yāmas.

The Bhagavata Purana identifies Yagya with Vishnu and Dakshina with goddess Lakshmi

Lakshmi

Lakshmi or Lakumi is the Hindu goddess of wealth, prosperity , light, wisdom, fortune, fertility, generosity and courage; and the embodiment of beauty, grace and charm. Representations of Lakshmi are also found in Jain monuments...

, the goddess of fortune and consort of Vishnu. After Yagya's birth, he lived at the house of his grandfather Svayambhuva Manu. The sons to Yagya and Dakshina are named as Tosha, Pratosha, Santosha, Bhadra, Sânti, Idaspati, Idhma, Kavi, Vibhu, Svahna, Sudeva and Rocana. They are collectively called as the Tushita gods. Later Yagya is described to become the Indra. Garuda Purana says that he performed many sacrifices.

Another tale from the Vishnu Purana tells at the time of destruction of Daksha

Daksha

In Hinduism, Daksha, "the skilled one", is an ancient creator god, one of the Prajapatis, the Rishis and the Adityas. Daksha is said to be the son of Aditi and Brahma...

's sacrifice (yagya), Yagya, the lord of sacrifice, was escaping as a deer. Yagya's head was severed by Virabhadra

Virabhadra

According to Hindu mythology, Virabhadra or Veerabhadra was a super being created by the wrath of Rudra , when he stepped in to destroy the Yagna of Daksha, after his daughter Dakshayani - consort of Shiva, self-immolated in yagna fire...

, a fierce incarnation of Shiva. Latter accounts in the Harivamsa

Harivamsa

The Harivamsha is an important work of Sanskrit literature, containing 16,374 verses, mostly in metre. The text is also known as . This text is believed as a khila to the Mahabharata and is traditionally ascribed to Krishna Dvaipayana Veda Vyasa...

 and Linga Purana

Linga Purana

The Linga Purana is one of the major eighteen Puranas, a Hindu religious text. The extant text is divided into two parts, comprising 108 and 55 chapters respectively. These parts contain the description regarding the origin of universe, origin of the linga, and emergence of Brahma and Vishnu, and...

 relate this to the origin of the constellation (Nakshatra

Nakshatra

Nakshatra is the term for lunar mansion in Hindu astrology. A nakshatra is one of 27 sectors along the ecliptic...

) Mrigashīrsha

Mrigashirsha

Sanskrit mr̥gáśiras the 5th nakshatra or lunar mansion as used in Hindu astronomy and astrology is the constellation Orion. Its position is described in the Surya Siddhanta....

 ("deer-headed"). The creator god Brahma

Brahma

Brahma is the Hindu god of creation and one of the Trimurti, the others being Vishnu and Shiva. According to the Brahma Purana, he is the father of Mānu, and from Mānu all human beings are descended. In the Ramayana and the...

 elevated the deer-headed Yagya to the planetary sphere as Mrigashīrsha.

Association with sacrifice

Vishnu has been equated to yagya ("sacrifice") as early as in the Vedas

Vedas

The Vedas are a large body of texts originating in ancient India. Composed in Vedic Sanskrit, the texts constitute the oldest layer of Sanskrit literature and the oldest scriptures of Hinduism....

. The commenter on the Vedas - Sayana

Sayana

' was an important commentator on the Vedas. He flourished under King Bukka I and his successor Harihara II, in the Vijayanagar Empire of South India...

 describes Vishnu as the lord of yagya or the sacrificer himself. Even the Bhagvad Gita associates Vishnu to yagya (sacrifice). Performing sacrifices is considered to equivalent to pleasing Vishnu. The Vishnu Sahasranama

Vishnu sahasranama

The Vishnu sahasranama is a list of 1,000 names of Vishnu, one of the main forms of God in Hinduism and the personal supreme God for Vaishnavas . It is also one of the most sacred and commonly chanted stotras in Hinduism...

("Thousand names of Vishnu") also relates Yagya as a name of Vishnu.