In Greek mythology, Ephialtes was one of the Aloadae, the pair of Thessalian giant brothers — the other being Otus — born to Iphimedia, wife of Aloeus, by the god Poseidon. Famed for their prodigious size and strength, the brothers grew at an extraordinary rate and dared to make war on the gods, threatening to pile mountain upon mountain to scale Olympus, with Ephialtes coveting Hera and Otus desiring Artemis. Their assault ended in death — by Apollo in some accounts, or on Naxos when Artemis tricked them into spearing one another. From their stepfather Aloeus they took the patronymic "Aloadae," and a euhemerized tradition later remembered them as Thessalian heroes and the first mortals to worship the Muses.
Adapted from Wikipedia, "Aloadae" · CC BY-SA 4.0
I.Family
Ephialtes and his brother Otus (or Otos) were the Aloadae, Thessalian sons of Princess Iphimedia, the wife of Aloeus, by Poseidon. Iphimedia is said to have induced the sea-god to make her pregnant by going down to the seashore and disporting herself in the surf, or by scooping seawater into her bosom.
From Aloeus — sometimes named as their real father — the brothers received their patronymic, the Aloadae. They had a sister, Pancratis (also called Pancrato), who was renowned for her great beauty, and the tradition also names sisters Elate and Platanus.
II.Mythology — War with the gods
The brothers grew at a prodigious rate and resolved to storm Mount Olympus and seize goddesses for themselves: Artemis for Otus and Hera for Ephialtes. To reach heaven they planned to pile mountains one upon another — Olympus is usually said to be the lowest, with Ossa set upon it and Pelion upon Ossa as the second and third — and they threatened to turn the sea into dry land and the dry land into sea.
In one episode the brothers contrived to kidnap Ares and hold him captive in a bronze jar, a storage pithos, for thirteen months. The stepmother Eriboea revealed the imprisonment to Hermes, who rescued the war god.
Their daring brought their destruction. According to Homer, the Aloadae were killed by Apollo before they had grown any beards. In another famous account, the brothers met their end on Naxos when Artemis changed herself into a doe and leapt between them; unwilling to let the quarry escape, they both hurled their spears at once and so killed each other. Other versions hold that Apollo struck them down during their assault on heaven, or that Otus attempted to assault Artemis, prompting the divine deception. Their sisters Elate and Platanus were changed into trees, a fir and a plane tree respectively.
III.Mythology — Other stories
Diodorus preserves a euhemerized version in which the Aloadae appear as Thessalian heroes. Sent by their father, they set out to recover their mother Iphimedia and their sister Pancratis, who had been carried off by Thracians. After defeating the Thracians they settled on Strongyle (later Naxos), but in the end killed each other in a dispute and were afterwards honored as heroes.
Pausanias records another tradition crediting the brothers as pioneers of religion and civilization: they were believed to have been the first of all men to worship the Muses on Mount Helicon and to consecrate that mountain to them, though they honored only three Muses — Melete, Mneme and Aoede. They were also remembered as founders of cities such as Ascra, receiving veneration in Naxos, Ascra and Aloïum.
IV.Paleontology
Otozoum, an ichnogenus of sauropodomorph dinosaur known from fossil footprints, was named after Otus, the brother of Ephialtes.