Garga muni was one of the greatest sages of Puranic times. He was better known as Garga muni. He was the son of Rishi Bharadwaja and Susheela. He was the family priest of the family of Nanda (the foster-father of Krishna).
There was another Garga who was the son of Rishi Angiras. This Garga was the chief astrologer of King Prithu. He had obtained astronomical knowledge from Ananta.
He named Krishna after receiving the name by meditation. From the Vishnu Purana and other Puranas, one understands that although basically of Brahmin origin, a branch of Gargas became Kshatriyas and migrated westwards and joined the Yavanas (i.e. Ionians/Greeks). This could be the reason that later day Indians referred to Greek mathematicians and astronomers as Gargacharyas.