Eris (Greek: Ἒρις, "Strife") is the goddess of strife and discord in Greek mythology. She is the daughter of Nyx, but has no father. She is the opposite of Harmonia, who is the goddess of harmony.
The Romans called her Discordia. In Roman statues of Discordia, and in other Roman art of her, she looks scary and ugly, and she is holding a knife. There are a few myths about this goddess, such as the one involving the golden apple.
Nowadays, there are some people who call themselves Discordians. This idea comes from a book called Principia Discordia, which was written by Greg Hill and Kerry Thornley in San Francisco in the year 1958 or 1959. The book says that Eris might not have been scary and ugly after all, but that she was just misunderstood.
The Principia Discordia describes the Discordian Society and its Goddess Eris, as well as the basics of Discordianism.