The next incarnations are the Manus. Within one day's duration of the life of Brahmā (which is calculated by our solar year as 4,300,000 x 1,000 years) there are fourteen Manus. Therefore there are 420 Manus in one month of Brahmā and 5,040 Manus in one year of Brahmā. Brahmā lives for one hundred years of his age, and therefore there are 5,040 x 100 or 504,000 Manus in the duration of Brahmā's life. There are innumerable universes, with one Brahmā in each of them, and all of them are created and annihilated during the breathing time of the puruṣa. Therefore one can simply imagine how many millions of Manus there are during one breath of the puruṣa.
The Manus who are prominent within this universe are as follows: Yajña as Svāyambhuva Manu, Vibhu as Svārociṣa Manu, Satyasena as Uttama Manu, Hari as Tāmasa Manu, Vaikuṇṭha as Raivata Manu, Ajita as Cākṣuṣa Manu, Vāmana as Vaivasvata Manu (the present age is under the Vaivasvata Manu), Sārvabhauma as Sāvarṇi Manu, Ṛṣabha as Dakṣasāvarṇi Manu, Viṣvaksena as Brahma-sāvarṇi Manu, Dharmasetu as Dharma-sāvarṇi Manu, Sudhāmā as Rudra-sāvarṇi Manu, Yogeśvara as Deva-sāvarṇi Manu, and Bṛhadbhānu as Indra-sāvarṇi Manu. These are the names of one set of fourteen Manus covering 4,300,000,000 solar years as described above.
Then there are the yugāvatāras, or the incarnations of the millennia. The yugas are known as Satya-yuga, Tretā-yuga, Dvāpara-yuga and Kali-yuga. The incarnations of each yuga are of different color. The colors are white, red, black and yellow. In the Dvāpara-yuga, Lord Kṛṣṇa in black color appeared, and in the Kali-yuga Lord Caitanya in yellow color appeared.
So all the incarnations of the Lord are mentioned in the revealed scriptures. There is no scope for an imposter to become an incarnation, for an incarnation must be mentioned in the śāstras. An incarnation does not declare Himself to be an incarnation of the Lord, but great sages agree by the symptoms mentioned in the revealed scriptures. The features of the incarnation and the particular type of mission which He has to execute are mentioned in the revealed scriptures.