The first expansion is Balarama, Baladeva. Nayam atma bala-hinena labhyaha. It is said in the Upanishad, "Atma, the Supreme Soul, cannot be understood without being favored by Balarama."
Balarama is sometimes misunderstood as the bodily strength, that "Without physical strength, nobody can attain the Supreme Personality of Godhead." But that is not the fact. Bala-hinena means one who is not favored by Balarama or Nityananda, he cannot make any progress to understand the Supreme Personality of Godhead. That is the real meaning, bala-hinena: "without the favor of Balarama."
Balarama is guru-tattva, and Balarama is present in this age as Nityananda. So bala-hinena labhyaha does not mean "without any physical strength." One has to get favor of Nityananda Prabhu. Nityananda Prabhu, katiya mohan, avadhya karuna sindhu katiya mohan, durlabha krishna-prema kare jare tare jana.
So this first expansion is Balarama. And from Balarama, then chatur-vyuha, Vasudeva, Sankarshana, Aniruddha… Pradyumna, Aniruddha. So the Sankarshana feature of the Supreme Personality of Godhead who is the controller of bhutendriya-manomayam. The five elements, bhuta, indriya, and the ten senses, and the mind. Sankarshana, Pradyumna, Aniruddha — they are different controlling Deities of the different functions of the mind, intelligence, ego.
———-Lecture Srimad Bhagavatam – 3.26.25, Bombay, 2-Jan-1975