The cult centers of Apollo in Greece, Delphi and Delos, date from the 8th century BCE. The Delos sanctuary was primarily dedicated to Artemis, Apollo's twin sister. At Delphi, Apollo was venerated as the slayer of Pytho. For the Greeks, Apollo was all the Gods in one and through the centuries he acquired different functions which could originate from different gods. In archaic Greece he was the prophet, the oracular god who in older times was connected with "healing". In classical Greece he was the god of light and of music, but in popular religion he had a strong function to keep away evil. Walter Burkert discerned three components in the prehistory of Apollo worship, which he termed "a Dorian-northwest Greek component, a Cretan-Minoan component, and a Syro-Hittite component."
Who was Apollo's twin sister?
Artemis