In the Dune universe, created by Frank Herbert, Leto Atreides II (10,207-13,725 AG) is a fictional central character in "Children of Dune" and is the title character of "God Emperor of Dune." He is son to Paul Atreides and Chani, twin to Ghanima and the grandson of Duke Leto Atreides I of Arrakis, for whom he was named.

Duke Leto Atreides I was killed in the Harkonnen/Imperial invasion of Arrakis. Leto Atreides II is the second child of Paul to bear the name Leto, the first was killed on Arrakis by the Emperor's Sardaukar.

Leto and his twin sister Ghanima are "pre-born", meaning that, as fetuses in their mother's womb, they were awakened to consciousness and to their genetic memories because of the spice ingested by their mother; thus, they are born as fully matured human beings in the bodies of infants. In "Children of Dune," Leto is not prescient to the degree that his fatherl was, but he senses the test his father faced - to embrace a prescient vision of the universe is to set the universe on that path, a terrible responsibility that comes with terrible power. At the end of "Dune Messiah," Paul forsook that responsibility by walking into the desert - his time as the Fremen messiah had shown him that he was not strong enough to be messiah/tyrant to the universe. Leto believes that he must face the same test.

At the same time, the Imperium Paul created is ruled by his sister Alia Atreides as regent. The horror of the pre-born, the reason the Bene Gesserit call them "abomination", is that they are easily possessed by the ego-memories of their ancestors. When Bene Gesserit awaken to their 'other memories' in the ritual of the spice agony, they are adults with fully formed personalities, and can withstand the inner assault of their forebears; the pre-born have no such defense. Like Leto and Ghanima, Alia was pre-born, and she succumbs to the pressure under an intense dose of spice. Among her ancestors is the Baron Vladimir Harkonnen, still hungry for revenge against his enemies, the Atreides. Alia is possessed by him, and unconsciously turns against the Atreides empire, plotting to kill Leto and Ghanima and to tear down the Imperium in a bloody civil war.

Leto faces the test his father refused to take, and embraces prescience, its visions, its attendant power, and the terrible price it will extract- to follow his vision, Leto will become a symbiote with the sandworm and rule for thousands of years, effectively immortal until humanity evolves enough to kill him. By doing so, he will set the universe on "The Golden Path", a future in which humanity's survival is assured. Following an assassination attempt by House Corrino Leto disappears into the desert leaving Ghanima behind. He finds Jacurutu, a sietch that has been forbidden to anyone by Fremen law. There he finds the means to live for millenia by merging with sandtrout into a new symbiotic form of being.

Independently, Leto and Ghanima both solve the problem of the pre-born. Leto constructs his own personality out of an executive committee of his ancestors; with all (the important ones) possessing him, none can possess him individually. As part of Leto's plan, Ghanima hypnotizes herself to believe that Leto was killed in the assassination; the intense mental discipline this demands builds a safe haven in Ghanima's mind for her own personality to safely develop.

At the end, following his test and his embracing of his vision, Leto returns to wrest the Imperium from Alia and take his rightful place as Emperor.

A little more than 3,500 years have passed, and Leto is now almost fully transformed into a Sandworm. He is almost invulnerable to physical damage; his single weakness that he shares with the sandworms, an intense vulnerability to water, is a secret. "Leto's peace" has kept the universe quiet for that time, and the entirety of human society has become an audience for him. He is their emperor; he is their god. His all-female army of Fish Speakers keeps order and acts as priestesses (according to Leto, a female army is a nurturing disciplinarian, while a male army is essentially predatory and always turns against its civilian support base in the absence of an enemy).

Desolate Dune is gone, nothing but a memory within the Oral Histories Leto has created and encouraged, replaced with verdant Rakis. Except for Leto, the sandworms are extinct. Arrakis even has a great river named after Duncan Idaho. All that is left of the "ocean without water" bahr bela ma is a preserve set aside for Leto alone. This remnant is called Sareer (Arabic for "bed"), which is about the size of California. The old institutions, the Bene Gesserit, the Bene Tleilax, the Spacing Guild, the houses Major and Minor, the Landsraad, the technocrats of Ix, and CHOAM, have all faded from power in the face of Leto's hydraulic despotism: since he has absolute control of a single element on which the whole universe depends, he has the universe in the palm of his hand, and ruthlessly enforces his simplistic order.

Leto has taken over the Bene Gesserit's breeding program for himself, the same program that produced his father, the Kwisatz Haderach. His Golden Path is nearly assured now, and 3,500 years of rule has begun to bore him. The trap of prescience is an existence without surprises; Leto is also such a long-lived creature that he has seen it all, especially with the help of his other memory. There is nothing left for him to do but to ensure that humanity will survive. To accomplish this, he has spent the last three millennia enforcing quiescence on humanity: people rarely travel, rarely fight in wars, rarely do anything but live and worship him; the millennia of repression create in humanity a deep and urgent need to explode upon the universe, scattering itself beyond the reach of any single tyrant.

Leto must find a solution in which he dies without destroying his people. If a god was to commit suicide, his worshippers would commit suicide with him. For a god to fade, so would his people. The only way Leto can die and not take his followers with him is in revolution, so he breeds for the person who will overthrow him: Siona Atreides, the daughter of his majordomo, Moneo. Siona is the first human to carry a gene that makes her invisible to prescience, and thus uncontainable by it. Since she cannot be seen in a vision, she cannot be controlled by a vision. The tyranny of prescience will end with her — humanity can never again be bound by a powerful prescient like Muad'dib or the God Emperor himself.

Siona's partner in revolution is Duncan Idaho, the constant companion of Leto throughout the long millennia. For his entire reign, Leto has had a ghola of Duncan in charge of his Fish Speaker army. The Duncans represent the old Atreides loyalty, along with everything vital in humanity, so something in the Duncans always rebels against the holy blasphemy Leto has created; many Duncans die trying to kill Leto. When Siona finally arrives, she finds in Duncan a justification for revolt.

Meanwhile, the rest of the universe is scheming to kill Leto as well. The Bene Tleilaxu try many ham-fisted schemes; the technocrats of Ix are smarter. They craft a human to seduce Leto. First they create Malky, a being of perfect evil, a devil to Leto's God. Malky is a charming Lucifer, and as ambassador to Leto's court he plumbs the depths of Leto's piety. In Dune Messiah, the Face Dancer Scytale reveals to a Reverend Mother that the Bene Tleilax created their own Kwisatz Haderachs, and discovered that Kwisatz Haderachs will die before becoming their opposites (and so can be killed by manipulating them into betraying themselves). Malky's purpose is to get Leto to turn on his holy creation, but he fails because the Ixians don't realize that Leto, more than anyone, knows the blasphemy he has created.

At the same time as Leto is breeding a psi-invisible human, Ix invents another solution: no-chambers. A no-chamber is an electro-mechanical construct that hides its contents from prescient vision. Inside the first no-chamber, the Ixians grow their next attempt: Malky's niece, Hwi Noree, who shall replace him as Ix's ambassador. Hwi is the opposite of Malky, a creature of pure goodness. Where Malky failed, Hwi succeeds. Leto falls in love with her, and plans to marry her. He is not alone in loving her, however, for his current Duncan has also fallen to her charms. By this chain of events, Leto weakens his godhood enough to allow Siona's revolt the possibility of success.

Leto planned to wed Hwi in what remains of an old Fremen village near the former Sietch Tabr, but changes his mind at the last instant to use the Museum Fremen's Tuono Village, the place where Moneo had sent Siona and Duncan in an attempt to keep the peace and keep Duncan alive, safe from the God Emperor's wrath. However, that is not to be.

The Royal Peregrination, the journey on foot for any of Leto's trips, to Tuono has all the appearance of a normal trip. However, Siona and Duncan, both well aware of the God Emperor's coming and his schemes to breed them, are primed for rebellion, not quiscent acceptance. Siona uses her power over Nayla, Leto's pet Fish Speaker, to set in motion his demise. At the point of the Sareer's guardian wall that opens to allow for the passage of the Idaho River, Nayla, caught in her faith in Leto, opens fire on the bridge with a lasgun, destroying it as Leto and Hwi are crossing, dropping them into the Idaho River. The water destroys Leto's sandworm body, decomposing it into the sandtrout that will lock up the water in their bodies, recreating the conditions for the sandworms to re-appear, each with a pearl of Leto's consciousness and adaptability inside it. Leto dies, his last vision that of the Golden Path, shining brightly in humanity's future. His total reign spanned 3509 years.

After Leto's death, driven by the Famine Times and the pent up desires of thousands of years of Leto's peace, humanity explodes out of the universe in waves of migration known as The Scattering, as predicted and forced by Leto's Golden Path.

The sandworms which once again travel Dune after Leto's death carry, in his words, "a pearl of his awareness locked forever in an endless dream." They (and Leto) are worshipped as the Divided God, and their existence keeps humanity locked on Leto's Golden Path. In Heretics of Dune, the Mother Superior of the Bene Gesserit Taraza (and her immediate successor, Odrade) manage to save one sandworm from Rakis before it is destroyed by the Honored Matres. The loss of all but one of the sandworms, nearly all of Leto II's 'pearls' of awareness, and the Priesthood which worshipped the Divided God, finally frees the universe of his prescient vision.

More than 1500 years after his death, Leto II is brought back as a ghola onboard the no-ship Ithaca. Even at a very young age, he shows signs that he may be more than he seems. During an assassination attempt, he somehow transforms into a small sandworm and defends himself before reverting to an innocent one-year-old. As he grows older, he displays an uncanny intelligence and is very withdrawn. Duncan Idaho, reflecting, says it was cruel to bring Leto II back without his twin sister, who was so much of the original Leto II's life. The effects of bringing the God Emperor back have yet to be seen.