The Vedic god of yajna is Vishnu without a doubt.
Shatapatha Brahmana:
Aitareya Brahmana:
Taittiriya Brahmana:
Mahabharata:
'O Brahmana, the gods even do not know me truly! As however, I have been gratified with you, I will tell you how I created the universe! O regenerate Rishi, you are devoted to your ancestors and hast also sought my protection! You have also beheld me with your eyes, and your ascetic merit also is great! In ancient times I called the waters by the name of Nara; and because the waters have ever been my ayana or home, therefore have I been called Narayana (the water-homed).
O best of regenerate ones, I am Narayana, the Source of all things, the Eternal, the Unchangeable. I am the Creator of all things, and the Destroyer also of all. I am Vishnu, I am Brahma and I am Sakra, the chief of the gods. I am king Vaisravana, and I am Yama, the lord of the deceased spirits. I am Siva, I am Soma, and I am Kasyapa the lord of the created things.
And, O best of regenerate ones, I am he called Dhatri, and he also that is called Vidhatri, and I am Sacrifice embodied. Fire is my mouth, the earth my feet, and the Sun and the Moon are my eyes; the Heaven is the crown of my head, the firmament and the cardinal points are my ears; the waters are born of my sweat. Space with the cardinal points are my body, and the Air is my mind. I have performed many hundreds of sacrifices with gifts in profusion.
(Vana Parva, Markandeya Samasya Parva, Section CLXXXVIII)
Yajna is also the 445th name of Bhagavan Vishnu in the Vishnu Sahasranama, His 677th name being ‘Mahayajna’. Many other names of His in the Sahasranama are also Yajna-related:
The Vishnu Sahasranama is found in the 149th chapter of the Anushasana Parva of the Mahabharata.
Bhagavata Purana:
Yajna is Vishnu’s seventh incarnation.
Then, in the seventh (incarnation), Yajña[24] was born of Ruci and Ākuti [Ākūti?]. He along with gods of whom Yama[25] was the first, protected the period assigned to the Manu called Svayambhū. (1.3.12)
Thus, the Vedic Yajna is Lord Narayana alone.
Jaya Shri Hari!
