A sage, married with Satyavati, daughter of King Ghadi.
Richika was already old and King Ghadi did not want to give him his daughter as a wife. He defined an impossible bride price – 1000 white horses with one black ear each. Richika got the horses from Varuna, the lord of the waters
Satyavati was also called Kaushiki. When Richika died, she followed him to heaven, but remained as river Kaushiki on earth. Today the river is called Koshi.
See Galava, he also had to find white horses with a black ear.
Read about Richika here