Short answers, pulled from the story.
Apollo is an Olympian deity in ancient Greek religion, son of Zeus and Leto and twin brother of Artemis. His domains include healing, prophecy, music, poetry, archery, protection of the young, and the founding of cities. He was regarded by the Greeks as the most beautiful of all the gods and was worshipped as the patron deity of the oracle at Delphi.
Apollo was born on the floating island of Delos in the Aegean Sea. His mother Leto gave birth there after being rejected by many lands out of fear of the god she carried. Apollo was born on the seventh day of the month Thargelion according to Delian tradition, or the month Bysios according to Delphian tradition.
Apollo killed the serpent Python in order to claim the oracle at Delphi as his own prophetic seat. In the Homeric Hymn, Python was a female serpent-dragon and a guardian of the Delphic Oracle. After killing her, Apollo was required to undergo ritual purification before he could properly assume his role as the oracular deity of Delphi.
The Delphic Oracle was Apollo's most influential prophetic sanctuary in Greece. The Pythia, Apollo's high priestess, received visions by breathing vapors rising from a spring inside the inner sanctuary called the Adyton. Kings, lawmakers, and city founders consulted the oracle before major decisions, and its authority extended across the Greek world and beyond.
The etymology of the name Apollo is not settled. The Doric form Apellon is considered more archaic and may be related to the festival apellai and the month Apellaios, both connected with initiations of young men. A Hittite form, Apaliunas, appears in the Manapa-Tarhunta letter, suggesting the name has pre-Greek, possibly Anatolian origins. The scholar R. S. P. Beekes proposed a pre-Greek proto-form reconstructed as Apallyun.
In Rome, Apollo was adopted largely intact from Greek religion, with his first temple dedicated in 431 BCE following a plague. In Celtic regions, he was identified with local healing and sun gods: Apollo Belenus in Gaul and northern Italy, Apollo Grannus as a healing spring deity, and Apollo Vindonnus as a healer of eye ailments with a temple in Burgundy. Augustus dedicated the temple of Apollo Palatinus on the Palatine Hill in 28 BCE.