Eris a Greek Goddess of Strife, she was a daughter of Nyx (the night),sister of Ares and a Mother of the Kakodaemones. She arrived uninvited to Peleus wedding and argue with Hera, Aphrodite and Athenea, an episode known as the ‘apple of discord’: “…she threw an apple through the door, saying that the fairest should take it. Juno [Hera], Venus [Aphrodite], and Minerva [Athene] claimed the beauty prize for themselves.” (Pseudo-Hyginus).
This is not the only episode were Eris is related to an apple. Athena gave a hint to Heracles about how to behave in front of strife. He found an apple in his way and tryed to smash it, but every time he tried to get rid of it, the apple grew bigger, so Athena said: “If you just leave it alone, it stays small; but if you decide to fight it, then it swells from its small size and grows large.’”(Aesop)
Hesiod talked about the existence of two Eris: one of evil nature that pushes humans towards violence and the other of competitive nature that encourage them to improve they nature:
“She pushes the shiftless man to work, for all his laziness. A man looks at his neighbour, who is rich: then he too wants work; for the rich man presses on with his ploughing and planting and ordering of his estate. So the neighbour envies the neighbour who presses on toward wealth. Such Eris (Strife) is a good friend to mortals.”
Today Eris is the name of the ‘dwarf planet’ discovered on 2005 that started the quarrel about whether Pluto was or not a planet, because Eris was bigger. Pluto finally changed it status, now considered a dwarf planet too.