Srimad Bhagavatam Canto 10, Chapter 14, Text 20

SB 10.14.20

suresv rsisv isa tathaiva nrsv api
tiryaksu yadahsv api te ’janasya
janmasatam durmada-nigrahaya
prabho vidhatah sad-anugrahaya ca
 
Translation: 
 
O Lord, O supreme creator and master, You have no material birth, yet to defeat the false pride of the faithless demons and show mercy to Your saintly devotees, You take birth among the demigods, sages, human beings, animals and even the aquatics.
 
Purport: 
 
Among the demigods Lord Krsna appears in such forms as Vamanadeva, among the sages as Parasurama, among human beings as Lord Krsna Himself and as Lord Ramacandra, and among animals as the boar incarnation. Lord Krsna 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.
Srimad Bhagavatam Canto 10, Chapter 14, Text 19
Srimad Bhagavatam Canto 10, Chapter 14, Text 21