Agrius

Agrius was the brother of Oreius whom together were called the 'Bear Twins'.

History
They were the illigitimate spawn of a woman whom Aphrodite commanded must marry, though she herself chose not to and fled to Artemis. Aphrodite put a trance on the woman to make her fall in love with a bear and thus she was cursed with monstrous children as well as the hatred of both the gods.

Both were described as being eight feet tall, wearing nothing but blue jeans, being covered in shag-carpeted thick brown fur, with claws for fingernails, feet like paws, snouts for noses, and all their teeth being pointed canines. Agrius was obviously the wiser (or at least more commanding) of the twins as he ordered his noticeably less intelligent brother to do various tasks including 'punishing himself' which entailed Oreius slamming his own head into an object or causing other bodily harm.

The Sea of Monsters
During the time of Percy Jackson's second year at Camp Half-Blood, the bear twins had found work with Luke Castellan who had aligned himself with Kronos. They traveled with him as his 'assistants' as he called them and followed him around the Princess Andromeda. When Percy Jackson, Annabeth Chase, and Tyson arrived unexpectedly, they first encountered these beasts and Luke told them their story.

While it is said that the Bear Twins like half-bloods for food, it is unknown if they have ever eaten an unlucky demigod. After Percy and his friends escape the ship and rescue Grover Underwood, they again encounter Agrius and Oreius. Luke duels with Percy while Agrius is in charge of holding Blackjack prisoner and Oreius is commanded to feast upon Annabeth and Grover. The timely arrival of Chiron and the Party Ponies (a group of wild centaurs) startles the monsters which allows Blackjack to slip out of Agrius' grip and kick him fatally in the head. Agrius travels to Tartarus just moments after his brother.