A lesser power like her sister Nike, Eris is responsible for a lot of trouble and confusion among the Olympians. It was by her side Titian Typhon rode into battle against Zeus, whose companion was Nike.
A particularly famous tale tells of the time Eris alone, of all the Olympians, was not invited to a big wedding celebration. It's said the incident begot a war that destroyed an entire city. Eris had given one of three golden Apples of Discord to a mortal prince in attendance, instructing the basher to present it only to the one most fair. Hera, Athena, and Aphrodite all began petitioning the mortal, each promising different rewards if he chose them. When he chose Aphrodite, who had offered him the love of the most beautiful mortal woman, he doomed his city to destruction and war: the fury of the other goddesses.
Eris doesn't always work against the rest of the pantheon, though. The other powers sometimes call on her to wreck vengeance over their sleights for them. This was the very fate of two mortals who'd made the mistake of saying they were more in love than Hera and Zeus.