Short answers, pulled from the story.
The Hecatoncheires were three monstrous giants in Greek mythology, each with fifty heads and one hundred arms. They were named Cottus, Briareus, and Gyges, and were the children of Uranus (Sky) and Gaia (Earth) in the standard tradition.
In Hesiod's account, the Hecatoncheires fought alongside Zeus and the Olympians against the Titans. Zeus released them from imprisonment, fed them nectar and ambrosia, and they hurled three hundred boulders to defeat the Titans, who were then imprisoned in Tartarus with the Hundred-Handers as their guards.
Homer's Iliad explains that Briareus is the name the gods use, while mortals call him Aegaeon. The seventh-century BC poet Cinaethon also knew both names, indicating this dual naming was part of an established tradition, not a Homeric invention.
Aegaeon's name derives from a Greek root associated with the sea and waves, and multiple ancient sources depict him as a sea deity. The poet Ion of Chios called him the son of Thalassa (Sea), Ovid described him as a sea god who could overpower whales, and according to Arrian, the Aegean Sea itself was said to be named after him.
The sources disagree. Hesiod and Apollodorus describe them as allies of Zeus who helped defeat the Titans. The lost epic Titanomachy, and the Latin poets Virgil and Ovid drawing on that tradition, depict Aegaeon as fighting on the side of the Titans against the Olympians.
Dante places Briareus in the Ninth Circle of Hell and again on the first terrace of Purgatory in his Divine Comedy, completed in 1320. Cervantes mentions him in Chapter 8 of Don Quixote, comparing his hundred arms to the whirling sails of a windmill.