Alcyoneus

Alcyoneus is one of the giants created by Gaea to destroy the gods. He is the giant equivalent to Pluto/Hades.

History
During the first Gigantomachy, Alcyoneas couldn't be killed as long as he was within his home territory, Pallene. During the war, Hercules fought him in battle and wounded him, but couldn't kill him until he dragged him out of Pallene using his great strength.

In 1941, Gaea manipulated Hazel's mom, Marie Levesque, into moving to Alaska, an area out of reach of the Olympian gods. Gaea would take control of Hazel's mother every night and forced Hazel to call up precious stones and metals on a phantom island off the coast. Her powers almost lead to the rising of Alcyoneus until Hazel sacrificed herself to put the giant back in the earth and sink the island.

He reformed several decades later and attacked a Roman legion that had gone up north to try and fulfill the Prophecy of Seven during the 1980s, but ultimately failed and lost the camps sacred symbol, the Roman standard, an eagle staff that held the power of Jupiter.

The Son of Neptune
Alcyoneus is first mentioned during a Senate meeting about the quest to free Thanatos in Alaska. Alcyoneus is the one waiting for them and Hazel tells Reyna this (as Hazel was the one that helped raise him). When asked how she knew this, Nico interrupts saying that he was the one giant created to defeat their father, Pluto.

Hazel, Percy, and Frank travel north to Alaska to rescue Thanatos, whom the Giant has chained. They arrive at his ice fortress with the help of Arion. The ice fortress looks exactly like Camp Jupiter, much to the surprise of the demigods. Hazel and Arion try and defeat the giant while Frank frees Thanatos and Percy fights an army of shades who use to be the soldiers Alcyoneus defeated. After freeing Thanatos, Frank joins the fight against the giant and saves Hazel by transforming into a bird and pecking at his eyes. Frank, Hazel, and Arion manage to defeat him, but can't kill him as long as he is in Alaska, so Frank used a rope to pull Alcyoneus ten miles into Canada with the help of Arion. Alcyoneus insults them at first, claiming he can't be killed in his territory until Frank informs him that he is no longer in his territory, but they are in Canada. Alcyoneus tried to run back to Alaska, but is stopped when Frank turns into an elephant and pushes him back, and he is eventually defeated by Arion and Hazel.

Appearance
Alcyoneus is described as being bigger than Polybotes, being over 30 feet tall. His skin looks like it is made of a metallic gold material. His legs however are rust colored dragon legs. His armor is made of platinum links and he has an iron staff the size of a totem pole. Being made from precious stones and metals, his body is covered in them, including stones in his red braided hair. Unlike other immortal beings who bleed ichor, Alcyoneus' blood is made from oil and it is said raw diamonds make up his heart. When Arion pulls him from Alaska, his golden skinned paled and became the color of brass.

Abilities
Not much is known about the true extent of Alcyoneus. He can command the shades in his ice fortress made from old members of the Fifth Cohort who had traveled there. He is also skilled with a staff, managing to fend off Hazel and Arion for a time, even when they were traveling at supersonic speeds. His strongest ability is that he won't die as long as he is in his territory (Alaska in The Son of Neptune). Not matter how badly he is damaged he will simply reform.

Trivia

 * It is possibly that Alcyoneus is the only giant that can be killed without the help of a god, as long as he is outside his territory. Arion is the offspring of two gods, but is never listed as being a god in The Son of Neptune or in mythology.