Conventionally, the ancient Olympic games began in 776 B.C., based on records of stade-length races. The victor of this first Olympic game was Koroibos of Elis, in Southern Greece [see Bb on the map]. However, the origins of the ancient Olympics go back to a time that is not well-documented, and so the actual date of the first Olympics is disputed.
The origins of the ancient Olympics interested the ancient Greeks, who told conflicting, history-laced, mythological aitia (origin stories).
One Olympic origins story is connected with one of the early members of the tragedy-ridden House of Atreus. Pelops won the hand of his bride, Hippodamia, by competing in a chariot race against her father, King Oinomaos (Oenomaus) of Pisa, in Elis. Oinomaos was the son of Ares and the Pleiad Sterope.
Pelops, whose shoulder Demeter had once had to replace when she accidentally ate it, conspired to win the race by replacing the king's chariot's lynch-pins with ones made of wax. These melted on the course, throwing the king from his chariot and killing him. After Pelops married Hippodamia, he commemorated his victory over Oinomaos by holding the first Olympic Games. These games either expiated his killing or thanked the gods for the victory.
According to Gregory Nagy, in "Chapter 4 Pindar's Olympian 1 and the Aetiology of the Olympic Games", Pindar, in his 1st Olympian Ode, denies that Pelops served his son to the gods at the infamous feast where Demeter absent-mindedly ate a shoulder chop. Instead, Poseidon abducted Pelops' son and repaid Pelops by helping him win that chariot race.
Another version of the origin of the Olympic games, also from Pindar, in Olympian X, attributes the Olympic games to the great Greek hero Hercules (Hercules or Heracles), who held the games as a thank offering to honor his father, Zeus, after Hercules had exacted revenge on King Augeus of Elis. Foolishly, Augeus had defaulted on his promised reward to Hercules for cleansing the stables.
Pausanias 5.7 says the Olympic origins lie in Zeus' victory over Cronus. The following passage elaborates this and also explains musical elements in the ancient Olympics.
[5.7.10] Now some say that Zeus wrestled here with Cronus himself for the throne, while others say that he held the games in honor of his victory over Cronus. The record of victors include Apollo, who outran Hermes and beat Ares at boxing. It is for this reason, they say, that the Pythian flute-song is played while the competitors in the pentathlum are jumping; for the flute-song is sacred to Apollo, and Apollo won Olympic victories.