There are many mythological creatures in the Percy Jackson book series, both good and bad. This article focuses on the good creatures (we can’t call them monsters!). Stay tuned for an article chronicling the worst mythological creatures found in the series! Let’s get right into the best Percy Jackson mythological creatures.


Rainbow is a hippocampus, a half-horse half-fish, who appears at the beginning of Sea of Monsters with two other hippocampi to help transport Percy, Annabeth, and Tyson to Luke’s ship of monsters. He is larger than the other hippocampi so is able to carry the cyclops Tyson easily. 

percy jackson rainbow hippocampus fontana di trevi rome.jpg

They become friends, and Rainbow rescues the characters multiple times throughout the book. Hippocampi were often depicted in Ancient Greek art, and are said to be the animals that pulled Poseidon’s chariot.


percy jackson blackjack tshirt.jpg

Blackjack is a black pegasus that Percy rescues from Luke’s ship at the end of The Sea of Monsters. He becomes a prominent character in The Titan’s Curse. Because Percy’s father Poseidon created horses, Percy can communicate with them, and Blackjack uses this to ask Percy to help mythical creatures in tough situations. 

Blackjack sticks by Percy’s side throughout the first series and in Heroes of Olympus as well. The original Pegasus was an immortal winged horse that sprung from Medusa’s neck when she was beheaded by the original Perseus in Greek Mythology. There is a constellation named after him.


Bessie is a half-cow, half-serpent creature that Percy rescues from a fishing net in The Titan’s Curse and calls Bessie. Bessie then follows Percy throughout his quest to save Annabeth and Artemis. 

Bessie is later revealed to be a very important creature called the Ophiotaurus, who when killed has the power to bring down the gods. Percy saves the creature again by pleading with the gods to keep it safe instead of killing it. In Greek Mythology, the Ophiotaurus was killed by an ally of the Titan army, but the body was retrieved by an eagle of Zeus before being burned.

Mrs. O’Leary

Mrs O’Leary is a tame hellhound who was previously owned by Daedalus. When Daedalus dies at the end of The Battle of the Labyrinth, he asks Percy to take care of her. She is very friendly and likes to play catch with a bronze shield and a combat dummy. Mrs. O’Leary can travel through shadows which makes her a valuable asset, but due to her large size Percy leaves her at Camp Half-Blood to be taken care of. 

Percy Jackson Athens Tour ; Acropolis, Acropolis Museum & Temple of Poseidon
9 hours
Group Type

She helps the demigods throughout Riordan’s books. Cerberus, the three-headed guardian of the underworld, is the only known hellhound in Greek mythology. However, hellhounds appear in various other mythologies including English folklore.


Festus is a bronze automaton dragon created by the Hephaestus cabin years before the series. In The Lost Hero, Leo repairs him and attaches his wings. He takes Leo, Piper, and Jason on their quest but is destroyed during a crash landing. 

Leo and the Hephaestus cabin reuse his head as the figurehead of the Argo II. During the demigods’ travels through Europe, Leo secretly rebuilds the body of Festus and uses him to defeat Gaea. 

In the third series, Trials of Apollo, Festus appears again. While there are no mentions of dragon automatons in Greek mythology, there are many other automatons created by Hephaestus including dogs, eagles, horses, and bulls.


Tempest is a storm spirit in the shape of a horse. In The Lost Hero, Jason uses his power from his father, Jupiter, to tame Tempest and ride him to battle the giant Porphyrion. In Mark of Athena, Jason and Percy, possessed by evil spirits, attempt to kill each other while riding their respective horses—Tempest and Blackjack. 

This scene is depicted on the cover of the book. In Greek Mythology, storm spirits, called “Anemoi Thuellai,” were controlled by the god of wind, Aeolus, and released when the gods desired to wreak havoc. They are occasionally depicted as winged men or horses.


In Son of Neptune, Hazel recalls seeing a beautiful tan horse with a black mane when she was a child in Alaska in the 1940s. She rescues him from the Amazons who had him in a cage. Arion helps Hazel, Percy, and Frank defeat the giant Alcyoneus and speeds them back to Camp Jupiter. 

7-Day Percy Jackson Mythology Trip
7 days
Group Type

He appears throughout the remaining books to help Hazel. In Greek Mythology, Arion is an immortal horse born when Demeter turns into a mare to escape Poseidon, who chases her as a stallion. He is known to be very swift and was once owned by Hercules.

Aurum and Argentum

Aurum and Argentum are Reyna’s automaton guard dogs, first appearing in The Son of Neptune. Aurum is made of gold and Argentum is made of silver. They can sense when someone is lying so are very useful to Reyna. 

They come when summoned and reappear often throughout Heroes of Olympus to help Reyna. These metal dogs may have been modeled after the gold and silver dogs owned by a king that Odysseus encounters in The Odyssey.