“I am immortal in my homeland, Frank Zhang! And thanks to your friend Hazel, my new homeland is Alaska. You cannot kill me here!”
-Alyconeus to Frank Zhang
Alcyoneus is the bane of Pluto. He was responsible for the Michael Varus disaster of the 1980's. When Hazel first lived, he was about to rise until Hazel Levesque delayed it, and got herself as well as her mother killed. He is also the eldest of the Giants.
Alcyoneus was the second of the giants to rise. He made his homeland in Alaska, the land beyond the gods. Alcyoneus could could not be defeated while he while in Alaska but the Canadian border was not far from his original camp ground.
In the book, Alyconeus has captured Thanatos, the god of death, and chained him in a cave so he can't escape. Meanwhile, Gaea's armies have taken The Doors of Death while Thanatos was no longer able to guard them. This granted the monster armies passage from Tartarus to the mortal world. It also gave them the ability to not die, or rather to reform within seconds of being struck down because the enemy controlled who came out of Tartarus once dead.
Percy Jackson, Frank Zhang, and Hazel Levesque were chosen by Camp Jupiter to journey to Alaska and defeat the giant. The three launched a quest and eventually with the help of Arion, the horse was able to knock out Alyconeus and drag him across the Canadian border. In that time, Percy Jackson sacrificed himself over a cliff to bring down a whole legion of Roman ghosts under Alyconeus's command. The eldest giant also lost hold of Thanatos as his prisoner when Frank burned away his chains with the stick that was the key to his life.Hazel eventually defeated Alcyoneus with the help of Frank and Arion.