“Bhismadeva says that Shri Krishna is the first Narayana. This is also confirmed by Brahmaji in the Bhagavatam (10.14.14). Krishna is the first Narayana. In the spiritual world (Vaikuntha) there are unlimited numbers of Narayanas, who are all the same Personality of Godhead and are considered to be the plenary expansions of the original Personality of Godhead, Sri Krishna. The first form of the Lord Sri Krishna first expands Himself as the form of Baladeva, and Baladeva expands in so many other forms, such as Sankarsana, Pradyumna, Aniruddha, Vasudeva, Narayana, Purusa, Rama and Nrsimha. All these expansions are one and the same Viṣṇu-tattva, and Sri Krishna is the original source of all the plenary expansions. He is, therefore, the direct Personality of Godhead. He is the creator of the material world, and He is the predominating Deity known as Narayana in all the Vaikuntha planets. Therefore, His movements amongst human beings are another sort of bewilderment. The Lord, therefore, says in the Bhagavad-gita that foolish persons consider Him to be one of the human beings without knowing the intricacies of His movements.
Avatara means “one who descends.” All the incarnations of the Lord, including the Lord Himself, descend on the different planets of the material world as also in different species of life to fulfill particular missions. Sometimes He comes Himself, and sometimes His different plenary portions or parts of the plenary portions, or His differentiated portions directly or indirectly empowered by Him, descend on this material world to execute certain specific functions. Originally the Lord is full of all opulences, all prowess, all fame, all beauty, all knowledge, and all renunciation. When they are partly manifested through the plenary portions or parts of the plenary portions, it should be noted that certain manifestations of His different powers are required for those particular functions. When in the room small electric bulbs are displayed, it does not mean that the electric powerhouse is limited by the small bulbs. The same powerhouse can supply power to operate large-scale industrial dynamos with greater volts. Similarly, the incarnations of the Lord display limited powers because so much power is needed at that particular time. For example, Lord Parasurama and Lord Nrsimha displayed unusual opulence by killing the disobedient ksatriyas twenty-one times and killing the greatly powerful atheist Hiranyakasipu. Hiranyakasipu was so powerful that even the demigods in other planets would tremble simply by the unfavorable raising of his eyebrow. The demigods in the higher level of material existence many, many times excel the most well-to-do human beings, in the duration of life, beauty, wealth, paraphernalia, and in all other respects. Still, they were afraid of Hiranyakasipu. Thus we can simply imagine how powerful Hiranyakasipu was in this material world. But even Hiranyakasipu was cut into small pieces by the nails of Lord Nrsimha. This means that anyone materially powerful cannot stand the strength of the Lord’s nails.
Similarly, Jamadagnya displayed the Lord’s power to kill all the disobedient kings powerfully situated in their respective states. The Lord’s empowered incarnation Narada and plenary incarnation Varaha, as well as indirectly empowered Lord Buddha, created faith in the mass of people. The incarnations of Rama and Dhanvantari displayed His fame, and Balarama, Mohini, and Vamana exhibited His beauty. Dattatreya, Matsya, Kumara, and Kapila exhibited His transcendental knowledge. Nara and Narayana Rsis exhibited His renunciation. So all the different incarnations of the Lord indirectly or directly manifested different features, but Lord Krishna, the primeval Lord, exhibited the complete features of Godhead, and thus it is confirmed that He is the source of all other incarnations. And the most extraordinary feature exhibited by Lord Sri Krishna was The internal energetic manifestation of His pastimes with the cowherd girls. His pastimes with the gopis are all displays of transcendental existence, bliss, and knowledge, although these are manifested apparently as sex love. The specific attraction of His pastimes with the gopis should never be misunderstood. The Bhagavatam relates these transcendental pastimes in the Tenth Canto. And in order to reach the position to understand the transcendental nature of Lord Krishna’s pastimes with the gopis, the Bhagavatam promotes the student gradually in nine other cantos.
According to Srila Jiva Gosvami’s statement, in accordance with authoritative sources, Lord Krishna is the source of all other incarnations. It is not that Lord Krishna has any source of incarnation. All the symptoms of the Supreme Truth in full are present in the person of Lord Sri Krishna, and in the Bhagavad-gita, the Lord emphatically declares that there is no truth greater than or equal to Himself. Although in other places the incarnations are described as Bhagavan because of their specific functions, nowhere are they declared to be the Supreme Personality. In this stanza, the word svayam signifies the supremacy as the summum bonum.”
Source: “A.C. Bhaktivedanta Swami Prabhupada (2014 edition), ” Srimad Bhagavatam”, First Canto, Chapter 9 – Text 18
A.C. Bhaktivedanta Swami Prabhupada (2014 edition), ” Srimad Bhagavatam”, First Canto, Chapter 3 – Text 28″