Little is generally known about Proteus, but he apparently wished to escape New Olympus and see it destroyed. In one of his attempts to escape the island, he murdered Taurus' father, but was subsequently imprisoned. During his stay in prison, he tormented Taurus by taking the shape of his deceased father.
When Goliath, Angela, and Elisa Maza arrived on New Olympus via Avalon's magic, Elisa was put with Proteus in prison. When Goliath attempted to rescue Elisa, Proteus assumed her form and tricked Goliath into rescuing him instead. He then took Elisa with him, while masquerading as Goliath, and tried to overload the island's power source to trigger an explosion while he'd escape the island. Elisa saw through Proteus's ruse and lead Taurus to Proteus as he was about to let the island blow up. Taurus managed to defeat Proteus and imprison him once more.
The Goliath Chronicles
Proteus eventually escaped once more and fled to Manhattan, where he tried to get revenge on Goliath and Elisa. He kidnapped Goliath and led Elisa, Angela, Hudson, and Taurus to different locations in New York by leaving clues behind. He eventually did battle with the three, and during the final moments of the battle, disguised himself as Elisa. Goliath managed to see through the disguise by asking him whether Elisa had ever doubted him. Proteus was taken by Taurus to prison yet again.
When fighting he transforms into a giant green cyclops.
Proteus is devious and sadistic manipulator who often uses his shapeshifting abilities to make others to his bidding. He often morphs into a large cyclops. His powers supposedly include turning into inanimate objects. He is also able to seemingly combine attributes of all his forms into a toothy giant gargoyle-beast with a tail-bludgeon and four arms.
- Proteus at GargWiki