In Greek mythology, the Erymanthian boar (Greek: ὁ Ἐρυμάνθιος κάπρος; Latin: aper Erymanthius) was a mythical creature that took the form of a "shaggy and wild" "tameless" "boar" "of vast weight" "and foaming jaws". It was a Tegeaean, Maenalusian or Erymanthian boar that lived in the "glens of Lampeia" beside the "vast marsh of Erymanthus". It would sally from the "thick-wooded", "cypress-bearing" "heights of Erymanthus" to "harry the groves of Arcady" and "abuse the land of Psophis".

The fourth labour of Heracles was to bring the Erymanthian boar alive to Eurystheus in Mycenae. To capture the boar, Heracles first "chased the boar with shouts" and thereby routed it from a "certain thicket" and then "drove the exhausted animal into deep snow." He then "trapped it", bound it in chains, and lifted it, still "breathing from the dust", and returning with the boar on "his left shoulder", "staining his back with blood from the stricken wound", he cast it down in the "entrance to the assembly of the Mycenaeans", thus completing his fourth labour. "When the king [Eurystheus] saw him carrying the boar on his shoulders, he was terrified and hid himself in a bronze vessel."

"The inhabitants of Cumae, in the land of the Opici, profess that the boar's tusks which are preserved in the sanctuary of Apollo at Cumae are the tusks of the Erymanthian boar, but the assertion is without a shred of probability."

In the primitive highlands of Arcadia, where old practices lingered, the Erymanthian boar was a giant fear-inspiring creature of the wilds that lived on Mount Erymanthos, a mountain that was apparently once sacred to the Mistress of the Animals, for in classical times it remained the haunt of Artemis (Homer, Odyssey, VI.105). A boar was a dangerous animal: "When the goddess turned a wrathful countenance upon a country, as in the story of Meleager, she would send a raging boar, which laid waste the farmers' fields."