Lunatic Discordia
We're going to have an interesting and different ladies-of-myth blog today thanks to this request: "I was wondering if you could tell us more about the Greek Trickster goddess Eris, and all her shenanigans. Eris is surprisingly popular and well-known in modern pop culture, considering that she wasn't particularly beloved during ancient Greek religion, so she's a neat topic to explore."
First of all, I have to disagree with you (good-naturedly, though), friend - Eris is definitely not a trickster goddess! In mythological terms, a trickster is someone who rebels against established rules, order or authority, usually through cleverness, and most often as a means toward creating, liberating or enabling something creative and new. Tricksters tend to cause problems and upheaval through their misbehavior, but that upheaval often has positive consequences, such as the creation or distribution of new things or the realization of flaws in the current order that can be corrected.
You could argue that the episode with the apple that leads to the Trojan War is kind of a trickstery move on Eris' part, but for the most part, she doesn't do all that stuff. She tends to operate within the rules of the universe, not outside them, and there's pretty much nothing positive that ever comes out of anything she does.
Eris is the ancient goddess of discord and strife - and not the fun kind of discord where things are just sort of disorganized and quirky and excitingly non-conforming, but the horrible awful kind where everyone violently hates one another and everything gets destroyed. The ancient Greeks were terrified of Eris, who represented the horrors of warfare, violence, hatred and cruelty, which she visited on humanity whenever she had the chance on her own, and which she could also come down to inflict on the orders of Zeus or Hera, who set her loose to punish miscreants that they believed deserved it. We talk a lot about how awesome mythological ladies are around here, and Eris is certainly awesome, but it's the original meaning of the word awesome here - inspiring fear and awe, and the feeling that maybe you're in over your head.
In case you were wondering how much the ancient Greeks did not like this goddess, the laundry list of her most common descriptions refer to her as "hard-hearted", "harsh", "cruel", "abhorred", "unwholesome", "relentless", "wrathful", "wearisome", "death-bringing" and about ten thousand other words meaning that she's terrible and everyone wishes she were not around. In fact, although her name is most often translated into English as "strife" or "discord" (especially since the name of her Roman equivalent, Discordia, grew into the latter word in English), other translations make the name closer to "hatred". She is literally hatred for other people personified.
Eris' scariness is established partially by her familial relations, which are a giant roster of ancient primordial powers and figures that represent horribleness and awfulness in varying ways. Hesiod lists her mother as Nyx, the primordial night, a goddess so terrifying that even Zeus in moments of greatest wrath refuses to cross her; Hyginus expands this to also list her father as Erebos, personification of darkness itself as well as a living part of the underworld. Her siblings include such un-favorites of humanity as Apate (goddess of deceit), Geras (god of old age), Ker (god of violent death), Momos (god of mockery), Moros (god of doom), Oizys (goddess of misery), Nemesis (goddess of punishment), the twins Hypnos and Thanatos (gods of unconsciousness and death), and of course the Keres, the blood-drinking dark sister-triad to the Moirai or Fates, who inflict doom upon soldiers in combat and drag dying men off the battlefield and into Hades to feast on. There are a few nice siblings in there, like Philotes and Misericordia, but they can't really prevent the entire family from being a sort of primordial soup of terror and human suffering.
As if her immediate forbears and siblings weren't scary enough, Eris also has children of her own, and among her brood there are no nice people whatsoever. Her list of children includes Dysnomia (goddess of anarchy), Horkos (god of punishing oathbreakers), Lethe (goddess of forgetfulness), Limos (god of famine), and Ponos (god of toil and work); and she is also responsible for bringing into the world several sets of multiple siblings bent on a single distressing task, including the Algea (in charge of causing pain), Amphilogiai (in charge of legal disputes), Androktasiai (in charge of manslaughter), Hysminai (in charge of brawling), Makhai (in charge of battles), Neikia (in charge of arguments), Phonoi (in charge of murder), and Pseudologoi (in charge of lying). My personal favorite of her brood is Ate, who is literally the goddess of bad ideas, and whose interference is responsible for almost every time a hero in Greek myth makes a dumbass decision that gets them killed.
Hesiod actually hated her collection of children (together referred to as the Lugra, meaning "banes") so much that he decided to poetically declare that they were the daimones of all bad things in the world that were originally sealed in Pandora's jar, thus literally making Eris and her children the worst things to ever happen to the universe.
At any rate, Eris' most famous tale is of course that of the beginning of the Trojan War, although in reality she isn't actually involved all that heavily. When Thetis and Peleus (later to be the parents of Achilles) are being wedded, which is a big deal to the gods because of the prophecy that Thetis' child will outshine his father and everyone's need to make sure they safely know who that father is so no one accidentally sires a super-baby, Zeus invites every deity in the pantheon except for Eris; no one gives an exact reason for this, but presumably they didn't want her there because, well, she's terrible and causes all of the problems in the world.
In ancient Greek hospitality terms, however, this was a massive slight to Eris' reputation and honor, and when she arrived and was refused entrance to the banquet, she instead hurled a golden apple through the doors into the middle of the feast. The apple was inscribed "to the fairest", and the ensuing fight between Aphrodite, Hera and Athena over who it was supposed to go to led to Paris acting as judge to choose one of them, which in turn led to Aphrodite rewarding him for choosing her by giving him Helen as a wife, which in turn touched off the entire gigantic Trojan War debacle.