We understand from the Brahma-samhita and Skanda Purana that Krsna is always surrounded by many thousands of goddesses of fortune. The gopis are all goddesses of fortune.
It is said in the Skanda Purana that out of many thousands of gopis, 16,000 are prominent, out of those 16,000 gopis, 108 are especially prominent, out of these 108 gopis, eight gopis are still more prominent, out of those eight gopis, Radharani and Candravali are even more prominent, and out of these two gopis, Radharani is the most prominent.
From Srila Prabhupada’s Krsna Book, ch. 32: Krsna Returns to the Gopis