Hyllus was a son of Heracles and Deianira and the husband of Iole. When Heracles was dying after being poisoned by Deianira, he charged Hyllus to marry Iole once he came of age.

By Iole, Hyllus had a son, Cleodaeus, and three daughters, Evaechme, Aristaechme, and Hyllis. Through Cleodaeus and his line, Hyllus became the ancestor of the later Dorian kings who would eventually succeed in the Return of the Heracleidae.

Zeus had originally intended Heracles to be ruler of Argos, Lacedaemon, and Messenian Pylos, but through the cunning of Hera the hero was supplanted, and his intended possessions instead fell into the hands of Eurystheus, king of Mycenae.

After the death of Heracles, his children, after many wanderings, found refuge from Eurystheus at Athens. When Eurystheus demanded their surrender and was refused, he attacked Athens, but was defeated and slain.

Hyllus and his brothers invaded the Peloponnesus, but after a year's stay were forced by a pestilence to quit. They withdrew to Thessaly, where Aegimius, the mythical ancestor of the Dorians whom Heracles had once aided in war against the Lapiths, adopted Hyllus and made over to him a third part of his territory.

After the death of Aegimius, his two sons, Pamphylus and Dymas, voluntarily submitted to Hyllus, who thus became ruler of the Dorians. The three branches of that people were named after these three heroes — Hyllus, Pamphylus, and Dymas. (According to the Dorian tradition reported in Herodotus, Hyllus was really an Achaean.)

Desiring to reconquer his paternal inheritance, Hyllus consulted the Delphic oracle, which told him to wait for "the third fruit" and then enter the Peloponnesus by "a narrow passage by sea."

Interpreting this as three years, Hyllus marched across the Isthmus of Corinth to attack Atreus, the successor of Eurystheus, but was slain in single combat by Echemus, king of Tegea. A third attempt under his son Cleodaeus and a fourth under his grandson Aristomachus were equally unsuccessful.

At last Temenus, Cresphontes, and Aristodemus, the sons of Aristomachus, complained to the oracle that its instructions had proved fatal. They were told that by "the third fruit" the third generation was meant, and that the "narrow passage" was not the Isthmus of Corinth but the straits of Rhium.

They built a fleet at Naupactus, but before sailing Aristodemus was struck by lightning (or shot by Apollo) and the fleet destroyed, because one of the Heracleidae had slain an Acarnanian soothsayer. The oracle bade Temenus offer an expiatory sacrifice, banish the murderer, and seek a guide with three eyes. He met Oxylus, a one-eyed Aetolian riding a horse, who made up the three eyes and was pressed into service.

The Heracleidae repaired their ships and sailed by way of Antirrhium to Rhium in the Peloponnesus. In a decisive battle they defeated and slew Tisamenus, son of Orestes, the chief ruler of the peninsula, and divided the territory by lot: Argos fell to Temenus, Lacedaemon to Procles and Eurysthenes (the twin sons of Aristodemus), and Messene to Cresphontes, while Elis had been reserved by agreement for Oxylus.

There is no mention of these Heracleidae or their invasion in Homer or Hesiod. Herodotus speaks of poets who had celebrated their deeds, but these were limited to events immediately following the death of Heracles. The story was first amplified by the Greek tragedians, who probably drew their inspiration from local legends glorifying the services rendered by Athens to the rulers of the Peloponnesus.

The conquest of the Peloponnesus by the Dorians, commonly called the "Return of the Heracleidae," is represented as the recovery by Heracles's descendants of the rightful inheritance of their hero ancestor. While the Dorians claimed a legendary hero as ancestor of their ruling families, the traditions are not regarded as entirely mythical: they reflect a joint invasion of the Peloponnesus by Aetolians and Dorians, the latter driven southward from their northern home under pressure from the Thessalians.