Argus

Argus is the one hundred-eyed security guard at Camp Half-Blood.

History
Argus was created by Hera and was her servant. His great service to the Olympians was to slay Echidna as she slept in her cave. Hera's defining task for Argus was to guard the white heifer, Io, a mistress of Zeus, from him, keeping her chained to the sacred olive tree at Argive Heraion. Hermes (in some versions Pan or Apollo) sang or talked to him until he was drowsy and then touched all of his eyes, putting him in a deep sleep, allowing Hermes to free Io. He was created by Hera and is very emotional about her.

The Lightning Thief
After Percy's battle with the Minotaur, he wakes up every now and then in the Big House. One time, he woke and saw Argus with eyes all over his body before losing consciousness again. Argus drives Percy, Annabeth and Grover out of Camp Half-Blood to start their quest. At the end of the book, Argus helps Percy to his cabin to pack his things.

The Sea of Monsters
When Percy first arrives at camp, he finds out that both Chiron and Argus have been fired. When Percy gets Luke to reveal to the camp that Chiron was innocent, it can be presumed that he was hired again along with Chiron.

The Titan's Curse
Late at night at Camp Half-Blood, Zoë Nightshade has a dream about Artemis, the Olympian goddess of the moon and the hunt, and demands to speak to Chiron, but Argus refused to allow her into the Big House. From what Grover told Percy, Zoë and Argus got into a verbal argument, including Zoë calling Argus a "boil-brained lout," until Chiron came. When Percy follows Thalia, Grover, Zoë and Bianca, Blackjack informs him that Argus was not driving the Camp Half-Blood van, but that Zoë was.

The Battle of the Labyrinth
Argus fought in the Battle of the Labyrinth. He was seen before the battle at a command tent with the Athena campers.

The Last Olympian
Argus drives the demigods out of Camp Half-Blood to meet Percy at the rendezvous spot in front of the Empire State Building in Manhattan, NYC before the Battle of Manhattan and goes back to defend camp. After Percy hears Rachel Elizabeth Dare took his Pegasus Blackjack to camp, Percy, Annabeth and Nico go after her. Argus came to greet them and they witnessed Rachel becoming the new Oracle of Delphi for Camp Half-Blood.

The Lost Hero
Piper McLean loses consciousness after Hera speaks through  the oracle,Rachel Elizabeth Dare to her, and she is taken to the camp's Big House. When she wakes up, she sees Rachel and Argus there. Argus is unhappy by Hera's disappearance and Rachel says that Hera created Argus and he is protective of her. He starts to cry, which Rachel says they try to keep him from doing since he nearly flooded the camp the last time, as said in the book.

The Demigod Diaries
In Leo Valdez and the Quest for Buford, Argus looks embarrassed that the Maenads got in Camp Half-Blood without him knowing it.

Personality
Since Argus virtually never speaks, not much is known about his personality. It is shown in The Lost Hero that he is very protective of Hera. It's unknown how he ended up at Camp Half-Blood, or whether it was of his own free will or if a god wanted him to do it. He is shown to be a man of rules, since he wouldn't let Zoë in to see Chiron in The Titan's Curse. He was also annoyed when he discovered that the gods wouldn't be 'riding to the rescue' in the Battle of Manhattan since he rolled his eyes when Percy told him.

Appearance
Percy describes Argus to look like a typical blond surfer dude, with the exception that he has a hundred blue eyes all over his body and supposedly has one on his tongue; which is the main reason why he doesn't talk much.

Trivia

 * Argus is one of the few supporting characters that made an appearance in all books, until The Son of Neptune.
 * In The Lost Hero it is said that Hera created Argus and as such, he is very protective of her.
 * When he rolls his eyes it looks like his body is swirling
 * Argus took part in The Battle of the Labyrinth as a guard of Athena cabin's command tent.
 * When he cries, it causes floods.