Hyperborean Giant

Hyperboreans are giants from the North. They are usually peaceful and described as having blue skin and icy gray hair. They appear only in the final book of the series.

In The Last Olympian
Hyperborean Giants are depicted in the final book in the Percy Jackson and the Olympians Series as oafish abominable snowmen that only serve Kronos due to their extreme gullibility. They fought in the Battle of Manhattan. In combat they prove to be quite a threat as they can freeze whatever foes they defeat in a block of ice. When wounded the Hyperborean giant will bleed blue blood, and when defeated will freeze in a block of ice itself. It is unknown if or how the giant would reach Tartarus from this state. Percy Jackson helped Annabeth Chase defeat a nasty Hyperborean Giant that was attacking the campers. He fought several others in the battle and a Hyperborean eventually fought and won a battle with Clarisse La Rue trapping her in an ice prison until she was rescued.

Known Hyperboreans
Only one Hyperborean Giant has been named throughout the entire series (though they only appear in the final book) and his character is only depicted in one scene with no major events accomplished or credited to his behalf. His name is Morrain.