Hesiod opens Works and Days by correcting his own earlier poem: there is not one Eris but two. The bad Eris, the one the Theogony already named among the children of Night, fosters war, quarrel and cruelty for their own sake, and no one loves her. The good Eris, whom Hesiod says Zeus set in the roots of the earth, is a harder and more useful power: she is the envy that sets a poor man to watch his rich neighbour plough and plant, and drives him to work his own land well in turn. Potter competes with potter, craftsman with craftsman, singer with singer, beggar with beggar, and the whole of human industry runs on that friction. Hesiod's two Erides are best read as one goddess split by a moral argument rather than as two separate figures with separate myths: the poet wants strife to be real and dangerous and, in one of its forms, also productive, and giving it two names lets him say both things about the same underlying force without contradiction.
The Homeric Eris, by contrast, keeps to the single, darker reading. In the Iliad she is Ares' sister, walking the battlefield beside him, small when she first appears and growing until she plants one foot on the earth and her head in the clouds, spreading Kakos Andrasi Neikea, evil strife, among the fighting men. This Eris has no interest in honest competition; she exists to make an already violent scene worse, and Homer never asks the audience to admire her the way Hesiod's good Eris asks to be admired. The two portraits were composed for different purposes and were never reconciled by any ancient source into a single consistent biography, and the atlas records them side by side rather than collapsing one into the other.