Apollo is the twin brother of Artemis and the son of Leto and Zeus. Born on the island of Delos, he is often referred to as 'the Delian Apollo', or as 'Phoebus Apollo', a name linking him to his grandmother, the Titan Phoebe.
Apollo is usually associated with the more civilized aspects of Greek society. While he was the god of plague, he was also the god of medicine and healing. He was the god of archery, but not associated with war or hunting. He was associated with music and poetry, usually holding his lyre, which was made by Hermes, and accompanied by the Muses. He was also the god of prophecy and oracles, since he could tell no lie. In later myths he also become associated with the sun, which had traditionally been the realm of Helios, the son of Hyperion.
Apollo's first task as a god was defeating the Python at Delphi. He defeated the serpent with only one arrow. Because of this, the famous Oracle at Delphi was dedicated to him. Later, he had to defend the oracle from Heracles, who wanted to destroy it after the Pythia refused to answer his question.
Perhaps his most famous son was Asclepius, whose mother was Coronis. Later, Apollo was told by a crow that she had been unfaithful. He then killed her for her infidelity. Regretting his hasty decision, he changed the crow, which had formerly been white, into its current black color. Asclepius was later struck down by a lighting bolt of Zeus. Apollo, angry at the undeserved death of his son, killed the Cyclops who had given Zeus the thunderbolt. Outraged, Zeus sentenced Apollo to serve a mortal man, Admetus, for one year..
Apollo played a major role in the Trojan War. He and Poseidon plotted to overthrow Zeus, and then become kings themselves. Zeus found out, and crushed their rebellion before it began. As punishment, Zeus forced Apollo and Poseidon to work for a mortal for wages. The man Zeus chose was Laomedon, the fifth king of Troy. Laomedon gave Apollo and Poseidon the task of building walls around Troy. Laomedon forced the pair to continue building greater and greater walls, giving Troy its legendary walls, which kept out the Greeks for ten years during the Trojan War. Upset by Laomedon's cruel treatment of them, Apollo sent a plague and Poseidon sent a sea monster to wreak havoc on Troy.
According to later tragedies (Homer writes nothing on this), before the Trojan War, Apollo fell in love with Cassandra, a daughter of Priam and Hecuba. Cassandra at first refused his advances. It was only after he promised her the gift of prophecy that she accepted. Once Cassandra had learned the art, she once again spurned him. Apollo was outraged, but a divine gift cannot be taken back. Therefore, Apollo instead cursed Cassandra. No matter how accurate her predictions, no one would ever believe her.
Because Apollo had a Trojan son, Troilius, with queen Hecuba, Apollo was the chief deity fighting alongside the Trojan during the war. He would rain plague-carrying arrows down upon the Greek camps. When Achilles returned to battle and is routing the Trojans, Apollo joined battle with Achilles, allowing time for the Trojans to escape back behind their great walls. After Achilles killed Hector, it was Apollo who guided Paris' arrow down upon the vulnerable heel of the great Achilles.
The Romans adopted Apollo into their pantheon without identifying him with any purely Roman god.