Atreyu is a Greenskin warrior from the Grassy Ocean in Fantastica.
Upon discovery that the Childlike Empress is dying, Atreyu is summoned to find a cure.
The Empress gives the AURYN to To Atreyu, a powerful medallion that protects him from all harm. At the advice of the giant turtle, Morla the Aged One, Atreyu sets off in search of an invisible oracle known as Uyulala, who may know the Empress' cure. In reaching her, he is aided by a luckdragon named Falkor, whom he rescues from the monster 'Ygramul the Many'. By Uyulala, he is told the only thing that can save the Empress is a new name given to her by a human child, who can only be found beyond Fantastica's borders.
As Falkor and Atreyu search for the borders of Fantastica, Atreyu is flung from Falkor's back in a confrontation with the four Wind Giants and loses AURYN in the Sea of Possibilities. Atreyu lands in the ruins of Spook City, the home of various wicked creatures. Injured by the fall and stranded in the dangerous city, Atreyu finds the wolf G'mork, chained and near death, who tells him that all the residents of the city have leapt voluntarily into The Nothing. There, thanks to the irresistible pull of the destructive phenomenon, they have become lies in the human world. The wolf also reveals that he is a servant of The Manipulators, the force behind The Nothing. They wish to prevent the Empress's chosen hero from saving her. G'mork then reveals that when the princess of the city discovered his treachery against the Empress, she imprisoned him and left him to starve to death. When Atreyu announces that he is the hero G'mork has sought, the wolf laughs and succumbs to death. However, upon being approached, G'mork's body instinctively seizes Atreyu's leg in his jaws. Meanwhile, Falkor retrieves AURYN from the sea and arrives in time to save Atreyu from the rapid approach of The Nothing.
Falkor and Atreyu return to the Childlike Empress, who assures them they have brought her rescuer to her—Bastian. But, Bastian decides to take over Fantastica for himself, and yet he is stopped by Atreyu, whom Bastian grievously wounds in battle.
In the first film, Atreyu is portrayed by Noah Hathaway.
While on their quest, Atreyu and his horse Artax reach the Swamps of Sadness, where Artax drowns in the swamps, leaving Atreyu disconsolate and alone; he reaches Shell Mountain, where Morla the Ancient One, a giant turtle, lives.
Morla tells Atreyu that the Southern Oracle might know how to stop the Nothing, but it was located 10,000 miles away. Believing that all hope is lost, Atreyu nearly drowns in the swamp but is saved by Falkor the Luckdragon.
When Atreyu wakes up, Falkor tells Atreyu that he has travelled 9,891 miles while unconscious, and has only 109 miles to go. After Atreyu and a gnome scientist, Engywook, witness a knight get blasted by the Sphinx Gate, Atreyu believes himself worthy, but soon starts to lose that faith after seeing the knight's skeleton. Atreyu jumps just as the sphinxes open fire, and makes it through safely.
Atreyu then reaches the Magic Mirror Gate. Here, he actually sees Bastian Bux, a boy who is reading the book. The Southern Oracle tells Atreyu that an Earthling child has to give the Empress a name. They also state, while collapsing, that only a human child can give the Empress the name.
As Falkor and Atreyu fly over the Sea of Possibilities, the Nothing attacks them; Atreyu gets knocked off Falkor and falls onto a beach near Spook City. Awakening without the AURYN, Atreyu comes across the forlong Rock Biter, grieving for his friends, who were swept away by the Nothing. Atreyu then encountered the Gmork, a wolf that was sent to kill Atreyu. Admitting that he was the warrior, Atreyu stabs the wolf with a stone slab, killing it.
The Nothing arrived and blows the remnants of the city away. Atreyu almost gets blown away, but is saved by Falkor at the last second. By this point, the Nothing has destroyed almost all of Fantasia, leaving the Ivory Tower intact.
Atreyu admits grief to the Empress, but she tells him that he hasn't failed his quest, because the earthling who has to give him a name is the same one reading the book. Bastian is shocked and believes that it's only a story, but the Nothing slowly destroys the Ivory Tower, knocking Atreyu unconscious.
Atreyu is last seen after Bastian recreates Fantasia; Atreyu is riding a newly-revived Artax.
In the second film, Atreyu is portrayed by Kenny Morrison.
In the novel, Atreyu is depicted as having olive green skin and blue hair.
- The makeup team on The NeverEnding Story planned to paint Noah Hathaway olive green just as Atreyu was in the book, but the effect didn't work, so they went without it. Hathaway later said, "It wasn't believable. I looked like fungi!"
- Atreyu is not mentioned and does not appear in The NeverEnding Story III: Escape from Fantasia for unknown reasons. the post hardcore/metalcore band atreyu is named after the character