After Frank Zhang managed 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 appeared on the battle field and claimed Frank. Mars gave Frank his M-16 which turned into a dragon tooth tipped spear when he learned that Frank hasn't learned his family gift. He told Frank that the spear has only three charges, and the spear was meant to give Frank enough time to discover his family gift.
When fighting a group of Basilisks outside Iris' R.O.F.L shop, Frank stabbed the spear into the ground and a Spartus emerged. Frank ordered 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 did not 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 out a rib from his chest and flung it like a knife, killing the last of the basilisks. While sinking back in the ground, Frank asked his name and he smiled when Frank asked if it is Gray.
Frank used the spear again when he wanted to distract a small group of Laistrygonian Giants. He told Gray to attack a small group of the giants and then lead them away as a diversion, but Gray only seemed to listen to the first part of the order and attacked the giants, stabbing them with the bones of his rib-cage and spreading their dusted remains so they could not reform. He then slipped back into the ground.
The last charge is used when a group of Gryphons knocked over a train in Alaska. Frank used Gray to defend a group of regular mortals. While Percy Jackson 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 had dissolved 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, barely kept in check by the power of Mars. While Mars gave him to Frank as a present, Frank constantly feared that if he doesn't keep the un-dead creature in check, it would kill him and anyone else who happened to be in the line of fire. He also seemed to take pleasure in fighting, as when Frank told him to act 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 did not affect 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 seemed to be the only being able to kill monsters longer than a few moments, as the Laistrygonian Giants and the Basilisks did not immediately reform like other monsters in The Son of Neptune. This may be because he scattered the dust they dissolved into.
- The spartus could only be summoned by driving the Dragon-Tooth Spear into the ground, which would call forth Gray.