She was the first female Imperial Sovereign. Born 151 years before Year 1, she was only 28 when she inherited the leadership of the government of Alfheim. Being underaged (Star Elves under 50 years old were mere children), Satei I's mother and the Council of Archons exercised a regency until she came of age 101 years before Year 1.
Unlike her father, she had a growing interest in offworld affairs involving Asguardia and further out in interstellar space. The fighting pitting First Colonies against each other and the Orks, plus the appeals from the Eskatonic Order for exploration of the wider universe, almost compelled Satei to support a unified interplanetary, interstellar regime.
By five years before Year 1, the Fundamental Laws outlining the constitutional framework for the new Star Imperium had been worked out. In Year 1, on Alfheim, the Council of Archons, the Council of the Clans, and representatives of the First Colonies proclaimed the new Star Imperium and the creation of the Imperial Parliament by the merger of the Councils of Archons and the Clans, with the new Committee for Granting Archon Status appointing many of the present representatives of the First Colonies with hereditary seats in the new Parliament.
In Year 12, Satei I abdicated her position as Sovereign, and joined the crew of a spaceship equipped with Hyperdrive and under the sponsorship of the Eskatonic Order. This ship intended to explore the universe as far as the galaxies of the Sculptor Group. However, the spaceship and all of it's crew and passengers disappeared. Their fate remains unknown even in the time of the United Planets, in the present Year 21,888.
Satei never married and had no children. According to the Fundamental Laws, a new Imperial Sovereign had to be elected by a majority in Parliament. Since Satei I, originally a supporter of the brand of Monotheism which viewed the Creator God as a Mother Goddess according to to the teachings of Thamar, but she later converted to Incarnatism and the worship of the Old Gods of the Star Elves (although she rejected the racism of Dark Elves). The majority was divided between the factions that became the Blue Monarchists and the Moderate Party. Satei's own parliamentary allies became the Red Monarchists.
The Council of Twelve in practice ruled the Star Imperium for 40 years, with the Asguardian Dwarf Dana Atrosos, appointed by Satei I as one of the first Imperial Viceroys, led the Imperium as one of it's Quasi-Sovereigns.