Hesiod's Theogony lists the Keres among the children of Night, born alongside other grim personifications, Doom, Blame, Sleep and Death itself, and the fullest surviving visual description of them comes from the Shield of Heracles, a poem attributed in antiquity to Hesiod, which pictures the Keres swarming over a battlefield, clothed in blood-soaked garments, quarrelling over the bodies of the newly dead and drinking their blood, their teeth gnashing as they fight one another for possession of each corpse. The image is deliberately horrific, presenting the Keres not as neutral psychopomps but as predatory, almost animalistic presences drawn specifically to violent, bloody death rather than to the peaceful end of an old age.
Homeric epic uses the related singular form, ker, somewhat differently, as a personal attribute: individual warriors in the Iliad are described as each carrying their own ker, a doom or fated death that will eventually catch up with them, most famously when Zeus weighs the kers of Achilles and Hector in golden scales before their climactic duel to determine, by which scale sinks, whose death is fated in that moment. This usage treats a ker less as an independent monstrous being encountered on a battlefield and more as an abstract, personified inevitability attached to each mortal individually, showing the concept operating at two related but distinct levels within Greek epic tradition.