Ichor originates in Greek mythology, where it is the ethereal fluid that is the Greek gods' blood, sometimes said to retain the qualities of the immortal's food and drink, ambrosia and nectar. Great heroes and demigods occasionally attacked gods and released ichor, but gods rarely did so to each other in Homeric myth.
Iliad V. 339–342
Blood follow'd, but immortal; ichor pure,
Such as the blest inhabitants of heav'n
May bleed, nectareous; for the Gods eat not
Man's food, nor slake as he with sable wine
Their thirst, thence bloodless and from death exempt. †
† We are not to understand that the poet ascribes the immortality of the Gods to their abstinence from the drink and food of man, for most animals partake of neither, but the expression is elliptic and requires to be supplied thus—They drink not wine but nectar, eat not the food of mortals, but ambrosia; thence it is that they are bloodless and from death exempt.
In Ancient Crete, tradition told of Talos, a giant man of bronze portrayed with wings. When Cretan mythology was appropriated by the Greeks, they imagined him more like the Colossus of Rhodes. He possessed a single vein running with ichor that was stoppered by a nail in his back. Talos guarded Europa on Crete and threw boulders at intruders until the Argonauts came after the acquisition of the Golden Fleece and the sorceress Medea took out the nail, releasing the ichor and killing him.
The Greek Christian writer Clement of Alexandria used "ichor" in the ancient medical understanding of a foul-smelling watery discharge from a wound or ulcer, in a polemic against the pagan Greek gods. As part of his evidence that they are merely mortal, he cites several cases in which the gods are wounded physically, and then adds, "And if there are wounds, there is blood. For the ichor of the poets is more repulsive than blood; for the putrefaction of blood is called ichor."