This is my entry for Mollinda's Myths and Legends Illustrative contest. [link]
The story of Artemis and Apollo's birth:
Zeus, husband+brother of Hera, God of the Sky, King of Heaven and all-around big guy decides to have a summer fling with Titaness Leto (sister of Asteria, daughter of Coeus). Hera, Goddess of Marriage and Zeus's wife, gets majorly pissed and curses Leto: she cannot give birth on land. Leto goes about her business until labour day, and she begs Hera for forgiveness. Hera shuns her, and refuses to send Eilithyia; (Goddess of Childbirth) to Leto. Unfortch for Hera, Leto finds a floating island by the name of Delos. There, she gave birth to her first child, Artemis. Artemis then helped Leto through 9 days and 9 nights of labour; and on the 10th day Leto gave birth to Artemis's twin; Apollo. After that rather nasty incident, Zeus chained the Isle of Delos to the bottom of the ocean; but it yet remains sacred to Apollo. Apollo and Artemis took upon themselves the duties of Helios and Selene; the Titans of the Sun and Moon. Artemis also became the Goddess of the Hunt and stayed a Maiden (ie. virgin). Apollo took upon Helios's duty as well as the additional perks of being God of Healing, Prophecy, Archery, Healing, Music, Poetry, and the Truth. (phew!)
Artemis's band of maiden followers became known as the Hunters of Artemis, and Apollo became the deity of Oracles.