Born as Siona Ibn Fuad al-Seyefa Atreides, she was the daughter of Moneo Atreides, the majordomo of God Emperor Leto II, and Fish Speaker Seyefa Nycalle, his commanded breeding partner. She was the end of Leto's long experiment in human evolution. In her, Leto had created the means of humanity's continued survival and of his own destruction.
In her first years, she remained with her parents in quarters near Leto's Citadel until she was ten, provided with training by her parents that was the groundwork for the education she would receive from her Fish Speaker teachers, and from Leto himself. She often accompanied Moneo on informal visits, held primarily on the Royal Road, avidly studying with curiosity and some religious awe the God Emperor, which amused him, as well as her evident ignorance of the fact that she was being studied in return.
When she was 10 years old, she was admitted to the Fish Speaker school at Onn. Seyefa died a year later of fever, with no one to care for her. Siona would blame Leto for this, as she was taken away to school at his orders, while he monopolized Moneo's time. It was the earliest event that would lead to her rebellion against him.
Despite her grief, she performed well during her training. Though she was primarily under the control of her instructors and the older students, she continued to be influenced by her father, and Leto. Her instructors were ordered to give her special attention, which she hated. Her errors were never overlooked, and never received a gentle reprimand, unlike her fellow students, but was required to repeat the entire sequence. More than any other pupils, and despite some at the faculty feeling uncomfortable about closely skirting heresy, Siona was exposed to the Oral History and its many contradictions of the official "received" version of events.
Siona's moods shifted as she entered adolescence, becoming increasingly cynical and critical. By her fifteenth birthday, there were reports about her conduct that alarmed her father. He visited her in secret to warn her that her heretical mockeries would lead to her destruction. The Welbeck Fragment records that meeting, where Siona tells her father that Leto always kills those close to him, and she wonders how Moneo survived that long.
During her last months at the school, Siona had made contact with outsiders from various walks of life, gingerly making advances in inquiry of potential insugents against the God Emperor's rule. Most were of Fremen descent, or else scholars familiar with their history and lifestyle, and thus sorrowful over its passing at Leto II's hands.
When she graduated, she organized a group of these like-minded rebels. During the first three years of this network, Siona's group gathered intelligence. Her biggest assets were her proximity to Fish Speaker Command, as well as her father, allowing her to know of appointments in the courtier's ranks, and maneuvered her friends accordingly. Furthermore, she was able to hide herself from Leto's prescience, enabling him to employ Ixian electronic sensors, and informers.
She often scolded her father for serving "the Worm." Moneo himself was in a difficult position professionally, and his warnings were scorned by her. Amused, Leto had plans for Siona, and insisted to Moneo that her struggle was "outside" him.
Eventually she came to think that violent action would be a necessity. In 13720, she gladly accepted Nayla, a strong and dependable person, not knowing that she was Leto's spy.
After long inaction, in 13723, Siona led a raid on Leto's Citadel in the Sareer. Everyone but her found their deaths by Leto's D-wolves, but she managed to steal a pair of Leto's journals and the complete plans of the Citadel. Sions sent the books off to the Spacing Guild, the Bene Gesserit, and the Ixians for attempted translation.
As Leto did with his breeding stock, he allowed Siona some "vacation" with her rebellion, and after he allowed her to receive and read the translated books, he decided she was ready to be summoned back to his stock. Her father brought her to the Little Citadel, and always worrying about her survival, he supplied her with a stillsuit. Leto already knew that his preparations would be isufficient.
Her trial would be to walk with Leto in the desert of the Sareer to the Citadel for eight days. Every night, she tapped at the front segment of Leto's pre-worm form, causing him to make a hammock of it for her. On her way, Siona was ignorant of the stillsuit-usage, and wasted her breath keeping the face-mask down. Leto talked to her, arguing about his right to rule, mentioning that the Fremen never wasted their breath and its moisture. Only then Siona realized she had to seal her mask, on the morning of the third day.
As Leto knew, by the fifh day, and with no water, Siona was near death. Driven by thirst (and the still-urgent need to understand Leto) Siona underwent the second phase of her testing, and overcame her fears of the spice trance. Directed by Leto, she stroked the flaps of the cowl clung about his face.
Drops of spice-essence-laced water fell to the surface of his skin, which Siona drank, and submitted herself into a ten-hour-long trance. This trance would reveal to her far more of the horrific future-that-might-be than anyAtreides other than Leto had ever beheld. The sight of those horrors sensitized her to the Golden Path, and she survived the ordeal, thus fulfilling Leto's demand.
Three days later, they completed their journey. At the Citadel, Siona was given new clothes, refreshment, and a brief rest, during which time she did not speak to Leto, before the two of them returned to Onn.
Even the sight of those horrors had not convinced Siona that Leto had been right to initiate the Golden Path. The knowledge of this latest encroachment on her personal life enraged her. When her father sent her to Tuono Village with Nayla and Duncan Idaho, intending to keep her as far away as possible from the God Emperor's wedding procession with Hwi Noree to Tabr. She left reluctantly, but then discovered that the ceremony's location had been switched to Tuono Village, giving her a chance to attack the God Emperor. As Leto and his company were traversing the Royal Road, her group ambushed them, and Leto, along with her father, fell from a massive bridge to their deaths.
Shortly after Leto II's death, Idaho destroyed the cell cultures from which the Duncan Idaho gholas were produced, supposedly ensuring that he would be the last.
Siona's rebellion, however, required more than the death of a tyrant. Duncan Idaho helped her to reassign and control the new powers released, and channel the new forces. The two wed in 10728, using the ancient ritual from the Oral History. Over the coming decades, Siona bore nine daughters and two sons, all who carried her ability to disappear from prescient view. She was thus the first of the new Atreides line.
Siona Atreides ingested spice to prolong her life, something that Idaho refused, as he had lived more than he deserved through his gholas. He died in 13791, and Siona retired from public life on Arrakis. She wrote her last book The Last Days, and died at the age of 255 years.