Vamana is the fifth incarnation of Vishnu, born as a dwarf into the household of a Brahmin priest.
Vamana tricked the demon king Bali to grant him as much of his empire as he could measure in 3 steps :
With the first step he covered all of Earth.
With the second step he covered all the heavens and while doing that Brahma washed his feet in his kamandula or water pot. Out of that pot, Ganga was born.
With the third step, Vamana pushed Bali back to the underworld or Patala Loka.