SB 10.1.24

vāsudeva-kalānantaḥ
 sahasra-vadanaḥ svarāṭ
agrato bhavitā devo
 hareḥ priya-cikīrṣayā
Word for word: 
vāsudeva-kalā anantaḥ — the plenary expansion of Lord Kṛṣṇa known as Anantadeva or Saṅkarṣaṇa Ananta, the all-pervasive incarnation of the Supreme Lord; sahasra-vadanaḥ — having thousands of hoods; svarāṭ — fully independent; agrataḥ — previously; bhavitā — will appear; devaḥ — the Lord; hareḥ — of Lord Kṛṣṇa; priya-cikīrṣayā — with the desire to act for the pleasure.
Translation: 
The foremost manifestation of Kṛṣṇa is Saṅkarṣaṇa, who is known as Ananta. He is the origin of all incarnations within this material world. Previous to the appearance of Lord Kṛṣṇa, this original Saṅkarṣaṇa will appear as Baladeva, just to please the Supreme Lord Kṛṣṇa in His transcendental pastimes.
Purport: 

Śrī Baladeva is the Supreme Personality of Godhead Himself. He is equal in supremacy to the Supreme Godhead, yet wherever Kṛṣṇa appears, Śrī Baladeva appears as His brother, sometimes elder and sometimes younger. When Kṛṣṇa appears, all His plenary expansions and other incarnations appear with Him. This is elaborately explained in Caitanya-caritāmṛta. This time, Baladeva would appear before Kṛṣṇa as Kṛṣṇa’s elder brother.