Hyperborean Giant

Hyperboreans are giants from the North. They are usually fearful (according to Thalia) and described as having blue skin and icy gray hair. They appear as friendlies in The Last Olympian but are relentless during The Son of Neptune.

Mythology
The Hyperboreans were mythical Giants who lived far to the North of Thrace. The Greeks thought that Boreas, The North Wind, lived in Thrace, and that therefore Hyperborea was an unspecified region in the northern lands that lay beyond the North Wind. Said to be friendly to mortals.

The Last Olympian
Hyperborean Giants are depicted as oafish abominable snowmen that only serve Kronos due to their extreme gullibility. They fought in the Battle of Manhattan. The Hyperborean Giant that accompanied Prometheus wore toy animals around his belt. 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. Percy helped Annabeth defeat a 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. Thalia recognizes them, since the Hunters of Artemis met a colony up in Alberta and got into a snowball fight with them.

Son of Neptune
When Percy, Hazel, and Frank arrive in Ancorage, Alaska they see Hyperboreans all over, wading through the forests, fishing in the bay, and striding through the mountains. Yet these are peaceful and invisible. They hid under one's thighs when the griffins attacked. The giant blew an ice cold wind which turned the griffins into "feathery Popsicle sticks".

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.

Trivia

 * They are similar to the frost giants of Norse mythology but something closer would be the monsters of destructions.