yaḥ sātvatāṁ kāma-dugho ’niruddhaḥ
yam āmananti sma hi śabda-yoniṁ
Ādi-caturbhuja, the original expansions from Baladeva, are Vāsudeva, Saṅkarṣaṇa, Pradyumna and Aniruddha. All of Them are viṣṇu-tattvas, or nondifferent Personalities of Godhead. In the incarnation of Śrī Rāma, all these different expansions appeared for particular pastimes. Lord Rāma is the original Vāsudeva, and His brothers were Saṅkarṣaṇa, Pradyumna and Aniruddha. Aniruddha is also the cause of Mahā-Viṣṇu, from whose breathing the Ṛg Veda appeared. All this is nicely explained in the Mārkaṇḍeya Purāṇa. In the incarnation of Lord Kṛṣṇa, Aniruddha appeared as the son of the Lord. Lord Kṛṣṇa in Dvārakā is the Vāsudeva expansion of the original group. The original Lord Kṛṣṇa never leaves Goloka Vṛndāvana. All the plenary expansions are one and the same viṣṇu-tattva, and there is no difference in Their potency.