Sun

Here the Lord informs Arjuna that this system of yoga, the Bhagavad-gītā, was first spoken to the sun-god, and the sun-god explained it to Manu, and Manu explained it to Ikṣvāku, and in that way, by disciplic succession, one speaker after another, this yoga system has been coming down. But in the course of time it has become lost. Consequently the Lord has to speak it again, this time to Arjuna on the Battlefield of Kurukṣetra.
(BG Introduction)

The pure devotee always has Kṛṣṇa within his heart; and with the presence of Kṛṣṇa, who is just like the sun, the darkness of ignorance is at once dissipated. This is the special mercy rendered to the pure devotee by Kṛṣṇa.
(BG 10.11 purport)

Of the Ādityas I am Viṣṇu, of lights I am the radiant sun, of the Maruts I am Marīci, and among the stars I am the moon.
(BG 10.21)

O son of Bharata, as the sun alone illuminates all this universe, so does the living entity, one within the body, illuminate the entire body by consciousness.
(BG 13.34)

I offer my respectful obeisances unto Śrī Kṛṣṇa Caitanya and Lord Nityānanda, who are like the sun and moon. They have arisen simultaneously on the horizon of Gauḍa to dissipate the darkness of ignorance and thus wonderfully bestow benediction upon all. Śrī Kṛṣṇa and Balarāma, the Personalities of Godhead, who formerly appeared in Vṛndāvana and were millions of times more effulgent than the sun and moon, have arisen over the eastern horizon of Gauḍadeśa [West Bengal], being compassionate for the fallen state of the world.
(CC Adi 1.84 – 86)