tiryakṣu yādaḥsv api te ’janasya
prabho vidhātaḥ sad-anugrahāya ca
Among the demigods Lord Kṛṣṇa appears in such forms as Vāmanadeva, among the sages as Paraśurāma, among human beings as Lord Kṛṣṇa Himself and as Lord Rāmacandra, and among animals as the boar incarnation. Lord Kṛṣṇa appears among the aquatics as Matsya, the gigantic fish. Indeed, the plenary expansions of the Supreme Personality of Godhead are innumerable, as the Lord relentlessly comes down within the universes to smash the false pride of the atheists and show mercy to the saintly devotees.
In another sense, the Lord never appears, since He exists eternally. His appearance is like that of the sun, which is always present in the sky but which periodically appears to our vision.