Phlegyas, son of Ares and Chryse, King of the Lapiths in Greek mythology was father of Ixion and Coronis, one of Apollo's lovers. Pregnant with Asclepius, Coronis fell in love with Ischys, son of Elatus. A crow informed Apollo of the affair and he sent his sister, Artemis, to kill Coronis. Apollo rescued the baby though and gave it to the centaur Chiron to raise. Phlegyas was irate and torched the Apollonian temple at Delphi and Apollo killed him.

In Book VI of Virgil's Aeneid, Phlegyas is said to have imposed a powerful tyrant upon the Lapiths, changed laws when given bribes, and to have raped Coronis himself, despite his anger at Apollo for having done so.

Phlegyas was condemned to act as ferryman for the souls that cross the Styx, one of the four rivers of Hades. In the Divine Comedy, the river forms the fifth circle of Hell, and Phlegyas ferries Virgil and Dante across it.

Phlegyas was the mythical ancestor of the Phlegyans .