Briareos as the “sea-goat” Aigaion
The sea-goat Aigaion “cannot be distinguished from Hesiod’s Briareos”, according to M.L. West; they are already explicitly linked in Iliad I.402-04, though they must have had separate origins:[3]

…the monster of the hundred arms whom the gods call Briareus, but mankind Aegaeon, a giant more powerful even than his father.”[4]
This episode, alluded to in Iliad (i.399ff), is found nowhere else in Greek mythology: at one time the Olympian gods were trying to overthrow Zeus but were stopped when the sea nymph Thetis brought one of the Hecatonchires to his aid, him whom the gods call Briareios but men call Aigaion (“goatish” Iliad i.403).[5] Hesiod reconciles the archaic Hecatonchires with the Olympian pantheon by making of Briareos the son-in-law of Poseidon, he “giving him Kymopoliea his daughter to wed.” (Theogony 817).

In a Corinthian myth related in the second century CE to Pausanias (Description of Greece ii. 1.6 and 4.7), Briareus was the arbitrator in a dispute between Poseidon and Helios, between sea and sun: he adjudged the Isthmus of Corinth to belong to Poseidon and the acropolis of Corinth (Acrocorinth) sacred to Helios.

In Virgil’s Aeneid (10.566-67), Aeneas is likened in a simile to “Aegaeon,” though in Virgil’s account Aegaeon fought on the side of the Titans rather than the Olympians; in this Virgil was following the lost Corinthian epic Titanomachy rather than the more familiar account in Hesiod.