kṛṣṇa, balarāma dui—caitanya, nitāi

Because Maha-saṅkarsana is the ingredient and efficient cause of the cosmic manifestation, He is present in every detail of it. Lord Caitanya therefore called Him His elder brother. The two brothers are known as Krsna and Balarama in the spiritual world, but at the present moment they are Caitanya and Nitai. Therefore the conclusion is that Nityananda Prabhu is the original Saṅkarsana, Baladeva.