|“||That’s what you said about our last stunt. I was hanging in that block of ice suspended over the River Lethe for six months, and we didn’t even get any media attention.||”|
During the first Gigantomachy, Otis and Ephialtes planned on reaching Olympus by stacking three mountains on top of each other. Ares planned on stopping them, but the twins managed to defeat the war god and place him inside of a huge bronze jar for thirteen months, until Hermes reluctantly saved him.
The twins were later defeated by the goddess of the hunt, Artemis. Artemis transformed herself into a deer, which the two wanted to kill. They both took aim with their spears and struck each other as Artemis ran between them.
In the Series
After Otis and Ephialtes were defeated, they began to make a home under the Colosseum in Rome. They began transforming it into their own hypogeum so they could one day destroy Rome. They also formed a pact with the monster Arachne. For centuries, they aided her in killing or capturing children of Athena who were given a quest to find the Athena Parthenos. The two also performed various stunts in order to gain media attention (normally at Otis' expense), but failed every time.
Percy Jackson dreamed that they were holding Nico prisoner in a bronze jar, similar to what they did to Ares in the original myth. The twins originally had planned to have Nico die on the Kalends of July, before he was rescued by the Seven. Otis and Ephialtes also teamed up with Arachne to destroy the "child of wisdom", referring to Annabeth Chase, and tried to keep Camp Half-Blood and Camp Jupiter ongoing enemies. They were battled by Percy and Jason Grace in the Colosseum, and were defeated by Bacchus.
It is mentioned by the Titans Hyperion and Krios, who are guarding the Doors of Death, that all the giants who were killed have reformed and returned to the mortal world through the Doors of Death, which includes Otis as well.
Otis and Ephialtes were among the giants assembled in the Athenian Acropolis, as seen in Piper's dream. Otis and Ephialtes fought the Seven Heroes of Olympus in the final battle of the Second Gigantomachy, and were ultimately brought down and killed by the combined efforts of Percy Jackson and Poseidon, with the latter spraying the giant twins out of the Parthenon with a high-powered water blast from his trident. Afterwards, Hades (invisible with his Helm of Darkness) opened up an abyss under the fallen giants' bodies, sending Otis and Ephialtes back to Tartarus.
Otis is shown to be somewhat less intelligent than Ephialtes, or at least he follows his brother's lead more often. While he tends to point out the flaws in his brother's plans or come up with ideas of his own, such as having a ballet number during the battle with Jason and Percy, his ideas are normally shot down for one reason or another. Like his brother, he goes to extremes for entertainment purposes, even if he normally gets the short end of the stick. Otis also loves to dance, and is quick to anger when people insult ballet.
Otis is only twelve feet tall, a respectable height for a cyclops, but only half as tall as most giants. He also looks somewhat more human than most of his brothers, since he has two green, yellow-eyed snakes for legs (which he usually conceals under his black pants). His long green hair is braided with golden and silver coins. He has his ten-foot spear strapped to his back. He looks almost identical to his brother Ephialtes, the only difference being their hair color.
- Prowess in Battle: In spite of being very short for a giant, Otis is a very strong and skilled warrior, though weaker than his brother Ephialtes. In The Mark of Athena, he successfully battled Jason Grace, one of the most powerful demigods in the world. However, Otis was swiftly defeated when Jason and Percy attacked him together (with his giant regeneration being the only thing that kept him from being killed instantly), and killed by an intervening Bacchus. Otis is swiftly overpowered again in The Blood of Olympus by the combined efforts of Percy and Poseidon.
- Giant Invincibility: As a giant, Otis can only be killed by a god and demigod together, as his armor and skin are regenerative and will heal during battle at an accelerated rate. However, he can also be killed by other giants, as seen when his brother Ephialtes accidentally did so in Percy Jackson's Greek Gods. He is brought down in The Mark of Athena by the combined efforts of Jason and Bacchus, and in The Blood of Olympus by the combined efforts of Percy and Poseidon.
- Ephialtes and Otis are the only two giants so far who share the same bane.
- They are also the only giants born to destroy a demigod, as Dionysus was a demigod when he originally defeated them.
- Otis loves ballet, something that infuriates his brother Ephialtes.
- As revealed in Percy Jackson's Greek Gods, Otis and Ephialtes are known as the Aloadae Giants.
- Otis is the more dim-witted twin between him and Ephialtes.
- In Greek mythology Ephiatles and Otis are demigod sons of Poseidon rather than gigantes.