Who is Hiranygarbha?
Is it a name of god? If yes, to which god it refers to?
What is the meaning of the word Hiranygarbha?
Hiraṇyagarbha literally translates as "the golden womb" and refers to the creator of the universe.
The Hiraṇyagarbha Sukta (Rig-Veda 10.121) identifies Hiraṇyagarbha as Prajapati i.e. Brahma:
In the beginning rose Hiranyagarbha, born Only Lord of all created beings. He fixed and holdeth up this earth and heaven. What God shall we adore with our oblation?
Giver of vital breath, of power and vigour, he whose commandments all the Gods acknowledge -. The Lord of death, whose shade is life immortal. What God shall we adore with our oblation?
Who by his grandeur hath become Sole Ruler of all the moving world that breathes and slumbers; He who is Lord of men and Lord of cattle. What God shall we adore with our oblation?
His, through his might, are these snow-covered mountains, and men call sea and Rasa his possession: His arms are these, his are these heavenly regions. What God shall we adore with our oblation?
By him the heavens are strong and earth is stedfast, by him light's realm and sky-vault are supported: By him the regions in mid-air were measured. What God shall we adore with our oblation?
To him, supported by his help, two armies embattled look while trembling in their spirit, When over them the risen Sun is shining. What God shall we adore with our oblation?
What time the mighty waters came, containing the universal germ, producing Agni, Thence sprang the Gods' one spirit into being. What God shall we adore with our oblation?
He in his might surveyed the floods containing productive force and generating Worship. He is the God of gods, and none beside him. What God shall we adore with our oblation?
Neer may he harm us who is earth's Begetter, nor he whose laws are sure, the heavens' Creator, He who brought forth the great and lucid waters. What God shall we adore with our oblation?
Prajapati! thou only comprehendest all these created things, and none beside thee. Grant us our hearts' desire when we invoke thee: may we have store of riches in possession.
The name 'HiraNyagarbha' is found in the HiraNyagarbhasukta of the Rig-Veda (10/121) that reads
hiraNyagarbhah samavartata agre bhtasya jatah patireka Asit/sa dAdhAra prithivim dyAm utemAm kasmai devAya habisha bidhema//
That SutrAtmA, in whose belly/womb ('garbha') the golden ('HiraNmaya') world (BrahmANda) is present. He is mentioned as the Lord ('Pati') of the world.
He is sometimes referred to as BrahmA : the creator form of God. In other places, He is also interpreted as the Primal Form of Brahman.
According t sanskritdictionary.com,(https://www.sanskritdictionary.com/?iencoding=iast&q=हिरण्यगर्भ&lang=sans&action=Search) the word means
the soul invested with the Sūkṣma-śarira or subtle body (Monier-Williams, Sir M. (1988)) a golden fetus (Monier-Williams, Sir M. (1988))
In his commentary on the Svetasvatara-Upanishad, Narayana defines HiraNyagarva as
hiraNyagarvam yasya brahmaNdam sariram, yadgarvo virAtpurusho brahmaNdapanchikritapanchabhutArabhdham ----meaning that HiraNyagarva means He, Whose body is the entire world, The All-pervading One Who holds everything within Him, and Who has created the five bhutas by the five tattvas.
Reference:Stavakusumanjaii, Swami Gambhirananda, Udbodhan, page 22, page 85.