|Appearances||The Son of Neptune|
|Quests||The Quest for Thanatos|
After Frank Zhang manages to be the first person over the wall of the enemy fort and win a war game (similar to Capture the Flag at Camp Half-Blood), Mars appears on the battle field and claims Frank. Mars gives him his M-16 which turns into a dragon tooth tipped spear when he learns that Frank hasn't learned the family gift. He tells Frank that the spear has only three charges, meant to give Frank time to discover his family gift.
When fighting a group of Basilisks outside Iris' R.O.F.L shop, Frank stabs the spear into the ground and a Spartus appears. Frank orders him to kill the basilisks. The skeleton warrior does as ordered, strangling one of the basilisks to death, being completely unaffected by the monsters poison. Another used its flaming breath on the warriors face, which didn't slow him down at all as he proceeded to walk over and crush the monster under his boot. The last attempted to flee, but the Spartus took a ribcage from his chest and flung it like a knife, killing the last of the basilisks. While sinking back in the ground, Frank asks his name and he smiles when Frank asks if it is Gray.
Frank uses the spear again when he wants to distract a small group of Laistrygonian Giants. He told Gray to attack a small group of the giants and then lead them away, but Gray only seems to listen to the first part of the order and attacks the giants, stabbing them with the bones of his rib-cage and spreading the golden dust so they can't reform. He then slips back into the ground.
The last charge is used when a group of Gryphons knock over a train in Alaska. Frank couldn't let the Gryphons attack the group of regular mortals and used Gray to defend them. While Percy admires that Frank used the last charge to help the people, he feels bad that the group was down another weapon. After using this charge, the spear used to call Gray vanished as well. It is unknown what happened to Gray as the group ran away, but he may have sunk back into the ground after the Gryphons were defeated.
Gray is a bloodthirsty killing machine. While Mars gave him to Frank as a present, Frank constantly fears that if he doesn't keep the un-dead creature in check, it would destroy him and anyone else in the line of fire. He also seems to take pleasure in fighting, as when Frank told him to ask as a distraction, he decided to attack and kill a group of Laistrygonian Giants instead.
As his name would suggest, Gray is mostly gray. His skin is a slightly transparent gray color and it is said his bones are gray as well. It is also said that his skin emits a kind of faint glow. He wears a muscle shirt, camouflage pants, and a pair of army boots.
Being dead, Gray is immune to poison and many other things. He may not feel any pain at all, as shown when the Basilisk venom didn't effect him even as it melted his flesh or when another burned his face with fire. He can pull out his own bones and use them as weapons, mostly relying on the bones of his rib-cage, which he uses as knives. He is an incredibly fast and efficient warrior, dispatching powerful foes in seconds.
- Gray seems to be the only being able to kill monsters longer than a few moments, as the Laistrygonian Giants and the Basilisks didn't immediately reform like other monsters in The Son of Neptune. This may be because he scattered the dust they dissolved into.
- The spartus could be activated by being thrown into to ground, thus summoning Gray, yet only for three times.
|Species:||Centaur | Cyclopes | Dragon | Drakon | Empousa | Giants | Harpy | Hyperborean Giant | Ichthyocentaur | Karpoi | Laistrygonian Giant | Pegasus | Skolopendra | Stymphalian Birds | Telekhine|
|Friendly Monsters:||Argus | Blackjack | Briares | Chiron | Don | Ella | Festus | Gleeson Hedge | Grover Underwood | Hippocampus | Mellie | Mrs. O'Leary | Ophiotaurus | Peleus | Scipio | Tyson | Tempest|
|Enemy Monsters:||Agrius and Oreius | Arachne | Basilisk | Charybdis and Scylla | Chimera | Chrysaor | Clazmonian Sow | Colchis Bull | Echidna | Euryale | Geryon | Joe Bob | Kampê | Manticore | Medusa | Minotaur | Nemean Lion | Polyphemus | Sphinx | Stheno | Typhon ||
|Neutral Monsters:||Cerberus | Erymanthian Boar | Gray Sisters | Gorgons | Furies | Flesh-Eating Horse | Gryphon | Hippocampus | Siren|