Koios was not extremely important in Greek Mythology like his brother Kronos was, however his descendants were the gods Apollo (god of poetry, music and many other things.. see page Apollo for more) and Artemis (goddess of the hunt and the moon).
He married his sister Phoebe. His daughter Asteria wasn’t well known in Greek Mythology. However, his other daughter Leto was the mother of the god Apollo and the goddess Artemis (As mentioned earlier). Koios was one of the four titans who held down his side of the cosmos (his father). Koios was a titan pillar. He was titan of the North.