The Gigantes (singular: Gigas) are the children of Gaea and Tartarus. They are the lesser brothers (and sisters) of the ancient Titans. They serve Gaea, their mother and one of the most powerful beings in the series. In The Lost Hero, Enceladus mentioned that each Olympian corresponded to at least one Gigas (probably more in fact as it was mentioned that there were at least 30 giants).
The Gigantes were not born until after the gods won the first Olympian War and took the throne from Kronos. While it was originally Gaea's idea for the gods to defeat her own children, the Titans, she grew unhappy with the way the gods ruled and hence gave birth to a new set of children with the primordial god of the pit Tartarus, the Gigantes.
Each Gigantes was born and bred specifically to oppose one of the Olympian gods, to usurp that god's domain. The King of the Giants was Porphyrion, the anti-Zeus, and he made an official declaration of war on the Olympians by kidnapping their queen, Hera though he fell in love with the queen of Olympus. It was prophesied that only a god and demigod working together could defeat this threat to Olympus, so Zeus called upon his own sons Hercules and Dionysus to help win the war, called the Gigantomachy.
First, Hercules manage to incapacitate Alcyoneus the eldest giant and anti Hades then dragged him out of his home country as Alcyoneus could only be killed if dragged out of his home territory. One by one, the Gigantes fell and all were killed except Aristaios, who was turned into a dung beetle by Gaea so the giant might be safe from the wrath of Olympus. The only way to get rid of a giant is for a god and demigod to work together against the giant.
After the fall of the gigantes, Gaea raised another child with Tartarus, a brutal storm giant named Typhon. At the sight of him, all the Olympians except Zeus fled. Zeus tried to put up a match but was outmatched and had his divine tendons tore out. Zeus later defeated Typhon with the help of several other gods by tricking the latter. After that, with her last and strongest son defeated Gaea officially fell back to her slumber and admitted defeat.
After the Second Olympian War, Gaea began to wake from her slumber and began to revive her Gigantes children to once again fight the gods. Enceladus, the giant that was born to defeat Athena, was one of the first of the gigantes to be brought back. He kidnapped Piper McLean's father, Tristan McLean, in order to force Piper to lead Jason Grace and Leo Valdez to their deaths. However, this plan failed when Piper told her friends about her father. Jason and Leo agreed to help her and Jason fought Enceladus and defeated him with the help of a lightning bolt from Zeus, Jason's father while Leo and Piper freed Piper's dad.
Gaea also managed to capture Hera, the Queen of the Gods, to use her power to revive Porphyrion, the King of the Giants as well as the one created to destroy Zeus, the King of the Gods. While his revival was a successful one, he was forced to retreat when Leo and Piper managed to set Hera free, for he dared not confront them as he was not at full strength and when Hera had demigods at her side.
Two more of Gaea's children are revealed to have been revived which are Polybotes and Alcyoneus. Polybotes was leading an army to Camp Jupiter, the Roman equivalent of Camp Half-Blood, in order to destroy the demigod children. He was created to destroy Neptune and showed that he had the ability to turn water into poison. He failed in his task however, as Percy managed to defeat him with the help of Terminus, the Roman god of borders.
Gaea's other child was Alcyoneus, Bane of Pluto. He was revived in part thanks to Hazel Levesque, a child of Pluto. Hazel was forced to help Gaea bring her child back, but eventually sacrificed her life in order to prevent his rise for a time. He can't be killed in his home territory and made his new home in Alaska, the largest state in America. He managed to capture Thanatos, God of Death, so that Gaea can revive her monsters almost instantly and bring more souls to the land of the living through the Doors of Death. He is defeated, however, when Arion, a mythical horse, helps Hazel and Frank Zhang pull Alcyoneus to Canada where they manage to kill him.
The two giants are revealed as Otis and Ephialtes, twin giants who were born to destroy Dionysus/Bacchus. The twins were stationed underneath Rome, preparing for the arrival of the Seven. They captured Nico di Angelo in a giant bronze jar to lure them into a trap. They had allied themselves with Arachne, who had been guarding the Athena Parthenos for centuries.
Percy Jackson, Piper McLean, and Jason Grace confront the twins in their underground lair. The twins activated their plan to destroy Rome in a glorious spectacle, but the heroes intervened. The giants nearly killed Jason and Percy before Bacchus appeared. He teleported them to a reconstructed version of the Colosseum where Jason and Percy faced Otis and Ephialtes for the god's amusement. The two eventually incapacitate the giants and Bacchus finished them off.
When Hazel Levesque meets Hecate, the goddess explains that her mortal enemy, Clytius, awaits Hazel and will only aid in his defeat should Hazel learn to master the Mist and arrive safely at the Necromanteion. Later, Leo dreams of being chased by Clytius and notices that the Gigante absorbs all of Leo's fire, leading to the conclusion that he must join Hazel in her fight.
While in Tartarus, Percy and Annabeth, led by Bob, met Damasen, the bane of Ares. He healed Percy from Gorgon poison and provided them with food to continue with their quest to the Doors of Death. As Percy fell asleep to recover, Annabeth paid Damasen by recounting their journey to defeat Gaea, and he explained that, as the opposite of the war god, he became peaceful, and was banished to Tartarus to participate in a never-ending fight with a drakon. Annabeth soon fell asleep and woke up only to overhear Damasen and Bob reflecting on their original statuses as foes, causing Annabeth to realize that the foes mentioned in the prophecy meant a Titan, Gigas, and demigod working together. Damasen, however, refused to travel with them as he feels he cannot escape his curse. Due to Polybotes' pursuit of Percy, the three continued on their journey.
As the heroes traveled to the House of Hades, Leo and Hazel were eventually separated from the others and find the Doors of Death, where Clytius and Pasiphaë were guarding the mortal side of the Doors. Hazel defeated the sorceress through the use of the Mist, just as Percy and Annabeth escape Tartarus thanks to Damasen's arrival to aid Bob in battling the physical manifestation of Tartarus. As the two reached the mortal world, Leo aimed a screwdriver to open the elevators, sprawling their unconscious bodies on the floor. Leo attempted to use his pyrokinesis but is quickly halted by the giant who boasts his victory. However, Hecate soon arrived and aided Hazel in combat against Clytius as Leo tended to Percy and Annabeth. Soon, the two are joined by Frank, Jason, Piper, and Nico, and together they are able to free the Doors of Death and destroy Clytius, but not before he reveals that all of his brethren have risen.
Due to the battle, the Necromanteion threatens to collapse, causing Hecate to briefly warn that Clytius was not lying when he announced the rise of all the Gigantes (excluding the recently destroyed Clytius and Damasen).
The first giant encountered in this book is Orion, The bane of Artemis and Apollo who has been sent to chase Nico di Angelo, Reyna Avila Ramirez-Arellano, and the satyr Gleeson Hedge while they are delivering the Athena Parthenos to Camp Half-Blood. Then, aboard the Argo II, in a dream, Piper sees Hippolytus, the bane of Hermes, who is telling Porphyrion that the Argo II is approaching Athens, where the giants are. When Piper and Annabeth go ashore to find the heartbeat of the chained god in Sparta, Mimas, the bane of Hephaestus and Ares, attacks them. However, Piper manages to release Phobos and Deimos and along with Piper, they proceed to defeat Mimas. Later, when Kymopoleia attacks the Argo II with a storm, Percy and Jason go underwater to find out why. Polybotes appears and incapacitates Percy with poison. Jason then promises to honor Kymopoleia and they defeat Polybotes. When the seven get to Athens, The gods appear in their Greek forms. Zeus and Jason defeat Porphyrion, Percy and Poseidon defeat Otis and Ephialtes, Athena and Annabeth defeat Enceladus, Piper and Aphrodite defeat Periboia, and Hazel, Frank, and Leo, along with the rest of the gods defeat the rest of the giants. In San Juan, Reyna, Nico, and Coach Hedge meet the Amazons and the Hunters of Artemis. Then, Orion comes and defeats almost one fourth of the Hunters and Amazons. Reyna and Hylla then fight Orion and he runs away. Then, in the Long Island Sound, Orion attacks Reyna. Bellona and Athena lend her strength and she defeats Orion.
In The Blood of Olympus, Piper mentions that there are at least 20 of them all together (without even counting Orion, Damasen, Mimas, and Clytius, none of whom were present), though not all of them have been portrayed and named in the series.
- Porphyrion - King of the Giants, Bane of Zeus/Jupiter - Defeated by Jason Grace and Zeus.
- Polybotes - Bane of Poseidon/Neptune - Defeated by Percy Jackson and Terminus, and then Jason and Kymopoleia.
- Alcyoneus - The Eldest Giant, Bane of Hades/Pluto - Defeated by Frank Zhang when he drags him out of Alaska, his homeland.
- Enceladus - Bane of Athena/Minerva - Defeated first by Jason and Zeus, and then by Annabeth Chase and Athena.
- Ephialtes and Otis - Banes of Dionysus/Bacchus - Defeated by Jason, Percy, and Bacchus, and then by Percy and Poseidon.
- Damasen - Bane of Ares/Mars - Defeated by Tartarus, his father.
- Clytius - Bane of Hecate/Trivia - Defeated by, Hazel, Frank, Jason, Nico, Piper, Leo, and Hecate
- Orion - Bane of Artemis/Diana and Apollo/Phoebus - Defeated by Reyna, Athena, and Bellona
- Hippolytus - Bane of Hermes/Mercury
- Mimas - Bane of Hephaestus/Vulcan - Defeated by Piper, Phobos, and Deimos.
- Thoon - Bane of the Fates - Defeated by the Fates.
- Periboia - Princess of the Giants, Bane of Aphrodite/Venus - Defeated by Piper and Aphrodite.
The Gigantes have some diverse personalities, for instance, Porphyrion, as the leader of the Gigantes, is proud and demands respect from all his siblings. His brothers, Otis and Ephialtes, are always seeking attention and making huge shows to gain it. Damasen, as the opposite to Ares/Mars, is a pacifist and a healer, living as a farmer instead of fighting against the gods.
However, they also share several traits. One of the main traits they share is their intense reverence for Gaea, their mother. This reverence for the Earth Mother have caused a rivalry between the Gigantes and their older siblings, the Titans, about who would Gaea let rule the world. Porphyrion and other Gigantes have claimed themselves to be superior to Kronos and the Titans several times.
- In most versions, the Gigantes were born with the the Furies, nymphs, satyrs, and Meliai when Ouranos' ichor fell on the Earth when Kronos chopped him up.
- Eurymedon is called the King of the Gigantes by Homer, but not much is known about him.
- In most myths, Orion, Otis and Ephialtes are demigod children of Poseidon.
- In the original myth, Damasen, Orion, Otis and Ephialtes weren't among the Gigantes who sought to destroy Olympus.
- In the series itself, Damasen admits he refused to take part in violence and stayed out of the war, and while it never directly mentioned, Orion's life story never hints that he fought either; in fact, he and Artemis were close friends.
- In the first four The Heroes of Olympus books, there are two main Gigantes featured:
- In The Lost Hero, Enceladus and Porphyrion were featured.
- In The Son of Neptune, Alcyoneus and Polybotes were featured.
- In The Mark of Athena, Otis and Ephialties were featured.
- In The House of Hades, Clytius and Damasen were featured.
- In The Blood of Olympus, however, all but Clytius and Damasen have reformed.
- There are more Gigantes than Olympians, suggesting that they were physically weaker.
- The giants were shown to be able to be defeated in single combat by demigods such as Hercules and Dionysus, even at full power.
- Although these Gigantes could be the counterpart of some minor gods. This has precedent in Clytius being born to oppose the minor goddess Hecate, Thoon being born to oppose the Fates, and the fact that Otis and Ephialtes were born to oppose a demigod Dionysus.
- Only the goddesses Hera, Hestia and Demeter do not have a Gigas counterpart in the series or myths.
- Although Enceladus mentioned that each Olympian corresponded to at least one Gigas, so is possible that actually Hestia, Demeter and Hera has a Gigas counterpart and are only not mentioned in both myths and in the series.
- Though Porphyrion and some others Gigantes claimed that they were superior to the Titans, this is clearly not true, as the Titans were showed to be stronger and harder to defeat than the Gigantes.
- Despite technically requiring a god and demigod working together to be killed, there are several instances of Gigantes being killed through other means. Alcyoneus was killed first by Hercules and later Frank, Hazel, and Arion simply by dragging him out of his home territory, Damasen was implied to have died at the hands of the primordial Tartarus alone while buying time for Percy and Annabeth to escape, Ephialtes and Otis died in a conflict seemingly separate from the First Gigantomachy wherein Artemis tricked them into attacking and killing each other, and Orion was killed long after the first Gigantomachy concluded by a giant scorpion sent by his mother Gaea after Apollo afflicted him with madness.
- In The House of Hades, Annabeth speculates that Bob, despite being a Titan rather than a god, might be able to help her and Percy kill any Giants they meet in Tartarus, though she seems doubtful about it being true. This ends up being confirmed later in the same book, when Hecate, technically a Titan herself, helps the rest of the Seven and Nico kill Clytius