Answer
The Supreme Reality is originally formless, unmanifest, and beyond the three qualities of material nature. In its primordial state, He alone exists; there is no second entity beside Him. That aspect of the Supreme is called Brahman.
“Ekam eva advitīyam.”
Meaning: “He alone existed, without a second.”
However, when the Supreme creates the manifested universe, He reveals Himself in a personal and manifest form as Narayana.
Not only this, at times He also descends in human form to protect dharma, destroy adharma, and delight His devotees.
In the Bhagavad Gita, Bhagawan Krishna says:
Avyaktaṁ vyaktim āpannaṁ manyante mām abuddhayaḥ Paraṁ bhāvam ajānanto mamāvyayam anuttamam.
Meaning: “The unintelligent think of Me, the unmanifest and supreme reality, as having merely assumed a manifest form. They do not know My highest, imperishable, and unsurpassed nature.”
The Lord further says:
Ajo’pi sann avyayātmā bhūtānām īśvaro’pi san Prakṛtiṁ svām adhiṣṭhāya sambhavāmy ātma-māyayā.
Meaning: “Although unborn and imperishable, and though I am the Lord of all beings, I manifest Myself through My divine power.”
And when people mistake this divine embodied form of God for an ordinary human being, the Lord says:
Avajānanti māṁ mūḍhā mānuṣīṁ tanum āśritaṁ Paraṁ bhāvam ajānanto mama bhūta-maheśvaram.
Meaning: “Foolish people disregard Me when I appear in human form. They do not understand My higher divine nature as the Supreme Lord of all beings.”
Thus, in the Gita, the Lord Himself describes both aspects of His reality: the unmanifest and the manifest, the attributeless and the qualified, the formless and the personal.
These are not two different Gods, but two aspects of the same Supreme Being.