The Last Olympian is a fantasy-adventure novel based on Greek mythology by Rick Riordan, published on May 5, 2009. It is the fifth and final novel in the Percy Jackson & the Olympians series and serves as the direct sequel to The Battle of the Labyrinth.  The Last Olympian revolves around the demigod Perseus Jackson as he leads his friends in a last stand to protect Mount Olympus. The book received many positive reviews.
The title refers to Hestia, the goddess of the hearth, who refers to herself as such in a conversation with Percy. This book is followed by The Lost Hero, the first book in a new series by Riordan, which is released on October 12, 2010.
Percy Jackson, his friends, and the Olympians fight in a war resembling the original war between the Greek gods and the Titans. Prometheus notes during a parley between him and Percy that the battle for Manhattan is like the Battle of Troy, except that now Olympus is Troy.
In order to try to head off Kronos's approach by sea, Percy and Beckendorf go to blow up his ship, the Princess Andromeda. However, Kronos is not caught off guard, and Beckendorf sacrifices his life to destroy the ship. Percy wakes up unaware of where he is, until he is awoken by his brother, Tyson. He finds he is in his father Poseidon's underwater palace which is under siege by the forces of the Titans. Percy wants to stay and help fight with his father, but he sends Percy back to Camp Half Blood.
Soon after arriving, Percy leaves again with Nico, son of Hades, to find out how he might stand a chance against Luke/Kronos when the time comes. After visiting Luke's mother and talking with Hestia, Percy procures a blessing from his mother, descends into the Underworld for the second time, and bathes in the River Styx like Achilles and Luke before him. He leaves Nico behind to convince his father to participate in the war (Demeter and Persephone have joined him in neutrality), and returns to the surface.
Percy organizes the demigod campers (minus the Ares cabin), and prepares for an urban battle. Before the battle starts, New York City is silenced by way of a powerful sleeping spell by Morpheus, god of dreams. Despite being joined by the Hunters of Artemis, satyrs, naiads, dryads, and other tree nymphs, Chiron's centaur cousins the Party Ponies, automatons fashioned by the late Daedalus, and the hellhound Mrs. O'Leary, Percy's forces are consistently forced back by sheer numbers. Kronos is not without losses, as Percy buffets the Titan Lord's brother, Hyperion into submission, from where Grover's nature spirits encase the Titan of the East in a massive maple tree.
Rachel, a mortal who can see through the Mist, flies from a family vacation to NYC (and strangely does not fall asleep) to tell Percy that he is not the hero of the Great Prophecy, and that it will influence his choice when he turns 16. More than that, she doesn't know.
Driven back to the blocks surrounding the Empire State building, Percy and his friends fight in a last stand to protect Mount Olympus from the massive army Kronos has amassed. Even when Hades arrives with his undead army, Kronos still manages to break through and enter Olympus.
Percy and Kronos battle in the throne room of Olympus, without either side gaining a significant advantage. Luke is shocked back into his normal self when Annabeth when he remembers his promise of family to Annabeth as he brutally smashes her across the throne room. The Great Prophecy hinges on Percy's decision to give Luke Annabeth's cursed dagger rather than attempt to kill Luke himself. Luke commits suicide by stabbing himself in his mortal point as Kronos struggles to reassert control, becoming the hero of the prophecy and ending the war on the dawn of Percy's 16th birthday.
With Poseidon ambushing Typhon at the Hudson River, the Olympians manage to send the demon down to Tartarus. Returning to the throne room, they grant Percy, Grover, Annabeth, Thalia, and Tyson rewards at the conclusion of their various quests. Percy, refusing godhood for himself, forces the gods to swear on the River Styx that they will recognize all of their children by the time they turn 13. At camp, new cabins are built for every god (including Hades and all the minor gods). Annabeth and Percy kiss underwater, their feelings for each other are solidified, and their relationship is cemented. Rachel Dare becomes the new Oracle and speaks the next Great Prophecy, Annabeth is promised to be the one rebuilding Mt Olympus in the future, and Grover becomes a Lord of the Wild and member of the Council of Cloven Elders. 
- Percy Jackson: The main protagonist and narrator of the first series. His status as a son of Poseidon, the apparent subject of the Great Prophecy, and yearly quests bring him to Olympus time after time. Like Luke has done, and Achilles before them both, he bathes in the River Styx and become invincible before he leads the Olympian-aligned forces in a defense of Manhattan, fighting on the varied fronts the entire time, even bringing down Hyperion, Lord of the East. For his heroism, particularly in saving Olympus from destruction, he is offered godhood, though he declines it in favor of his friends, whom he values before all else. His relationship with Annabeth solidifies against all odds during the battle and is set in stone underwater in the lake of Camp Half Blood.
- Annabeth Chase: One of Percy's friends, and by far his most trusted one. She is the 16 year old leader of the Athena cabin in Camp Half Blood. At the end of the book, she finally becomes Percy's public girlfriend, and is also given permission to redesign Olympus in the wake of Kronos's destruction.
- Grover Underwood: One of Percy's best friends. He first appeared in The Lightning Thief, and Percy has had to rescue the hapless satyr many times. He replaces the deceased Pan as a Lord of the Wild and member of the Council of Cloven Elders. He sets out to restore the Wild at the end of the series.
- Luke Castellan: A demigod of Hermes, as well as his father's pride and joy. Though he is the primary antagonist throughout the entire series and even hosts Kronos's spirit, he sacrifices himself to disperse Kronos's essence at the end of the book. In a way, he is the actual hero of the Great Prophecy.
- Tyson the Cyclops: Percy's half brother. Tyson leads fellow Cyclopes into battle and is rewarded a new club for his leadership.
- Rachel Elizabeth Dare: One of Percy's friends and competes with Annabeth for Percy's confused attention. She is a mortal who can see through the mist. She becomes the next Oracle of Delphi near the end of the book, 'dumping' Percy as a result.
- Nico di Angelo: A son of Hades. Though he seemed quite immature for his age when introduced two books earlier, his current 12-year-old self has matured rapidly over the course of a 2-year course of pain and loss. He is instrumental in convincing Hades to assist Percy in the defense of Olympus, and has become a powerful hero in his own right.
- Thalia Grace: Daughter of Zeus and leader of the huntresses of Artemis. She and the hunters come to assist Percy in the defense of Olympus, but when Annabeth, Percy, and Grover go to stop Kronos from destroying Olympus, she is trapped under a statue of Hera.
The Last Olympian received overwhelmingly positive reviews. Publishers Weekly wrote "...fans will not be disappointed" and remarked "As the capstone to this beloved series, this story satisfies." They praised Percy's "brave leadership" and said that "the final clash would keep a Hollywood special effects team busy for years." Booklist's starred review commented that "...Riordan’s imagination soars in the climactic battle scenes" but said that he manages to "bring the whole series to a satisfying close in the down-to-earth conclusion." It also received starred reviews from Kirkus.
Awards and nominations
Script error The unabridged audiobook version of The Last Olympian is read by Jesse Bernstein and was released on May 12, 2009 by Random House/Listening Library.