In Greek mythology, Polyidus was the wisest man in Lycia.

He told Bellerophon how to find and tame Pegasus in order to kill the Chimera.

One day, Glaucus, son of King Minos and Queen Pasiphae of Crete, was playing with a ball or mouse and suddenly disappeared. His parents went to the Oracle at Delphi who told them "A marvelous creature has been born amongst you: whoever finds the true likeness for this creature will also find the child."

They interpreted this to refer to a newborn calf in Minos' herd. Three times a day, the calf changed color from white to red to black. Polyidus observed the similarity to the ripening of the fruit of the blackberry plant and Minos sent him to search for Glaucus.

Searching for Glaucus, Polyidus saw an owl driving bees away from a wine-cellar in Minos' palace. Inside the wine-cellar was a cask of honey, with Glaucus dead inside. Minos demanded Glaucus be brought back to life, though Polyidus objected. As Minos hugged his son's corpse, a snake appeared nearby; Polyidus killed it with Minos' sword. Another snake came for the first, and after seeing the dead snake, the second serpent left and brought back an herb which then brought the first snake back to life.

Minos refused to let Polyidus leave Crete until he taught Glaucus everything he knew. Polyidus did so, but then, at the last second before leaving, he asked Glaucus to spit in his mouth. Glaucus did so, giving Polyidus back everything he had been taught.