The most famous tale of Eris ("strife") recounts her initiating the Trojan War. The goddesses Hera, Athena and Aphrodite had been invited along with the rest of Olympus to the forced wedding of Peleus and Thetis, who would become the parents of Achilles, but Eris had been snubbed because of her troublemaking inclinations.
She therefore tossed into the party a golden apple inscibed "Kallisti" -- "For the most beautiful one", or "To the Prettiest One"-- provoking the goddesses to begin quarreling about the appropriate recipient. The hapless Paris, Prince of Troy, was appointed to select the most beautiful. Greek mythological morality being what it was, each of the three goddesses immediately attempted to bribe Paris to choose her. Hera offered political power, Athena skill in battle, and Aphrodite the most beautiful woman in the world, Helen, wife of Menelaus of Sparta. Paris was a red-blooded young man, and while the length of time he meditated on this problem is not recorded, he did eventually award the apple to Aphrodite.
Eris has been adopted as the matron deity of the modern Discordian religion. In the process, however, she has lightened up considerably in comparison to the rather malevolent Graeco-Roman original.