Name: Eris (Greek: Ἔρις)
Sphere of influence: Strife
Famous portraits: She appears on some vase-paintings but not sculptures
This goddess is the personification of strife in classical Greek mythology, and as such her background is a bit shady. Different classical sources give different explanations to her, her background and her personality.
The oldest text to say much about Eris is the Work and Days, by Hesiod. According to him Eris was the daughter of a son of Cronus and her mother was Nyx. Her role was to cause strife among people - which, Hesiod stresses, was not necessarily a bad thing. It made man work harder to be better than his neighbours and generally prevented people from slacking off. Hesiod is less kind on Eris in his other work, Theogony. There he makes a long list of all those terrible children Eris gave life to, including Hysminai (combat), Neikea (quarrel) and Dysomnia (Lawlessness). Who the father was supposed to be is not known.
Homer on the other hand mentions her in the Iliad (book IV) but there calls her the sister of Ares (which would make her the daughter of Zeus and Hera). Some has taken this as a sign that there are two different goddesses, both named Eris and with the same function - to cause discord among men. A more likely explanation is that her lineage was not exactly written in stone - a common thing among lesser gods and goddesses - and might have changed over the years and with different traditions.
Eris is perhaps most famous for causing the Trojan War. She had not been invited to the wedding of Thetis and Peleus and as a revenge she came anyway and threw a golden apple into the crowd. On it she had written 'To the most beautiful' and of course the goddesses started to quarrel who was to recieve it. They decided on letting Paris choose among them, trying to bribe him with different gifts. Aphrodite, offering the fairest woman in the world (Helena), won - but since Helena was already married a war broke out (or so the story goes anyway).
This painting is from some Athenian painted pottery, dated to 575-525 B.C. - and even has the goddess' name written out.