The Eternal Empire is a large galactic government based on the planet Zakuul and founded by Valkorion. The Empire possesses a large fleet capable of battling both the Galactic Republic and the Sith Empire. It serves as the main antagonist organization in Star Wars: The Old Republic: Knights of a Fallen Empire.
Between the First Jedi Purge and the Great Galactic War, Sith Emperor Vitiate searched through the Wild Space in search of the Eternal Fleet, a supposedly unstoppable fleet of warships operated by sentient droids. His journey brought him to Zakuul, where he discovered a culture of superstitious humans who worshiped a group of deities called "Old Gods". Taking on the identity of "Valkorion", he unified the nomadic tribes of Zakuul into the Eternal Empire and installed himself as their Immortal Emperor. He formed a new Order of Force-users called the Knights of Zakuul who would rise above the light and dark sides of the Force. Soon the Eternal Fleet was located by the Scions, a subgroup of the Knights. The Eternal Empire soon gained control of the Eternal Fleet and the GEMINI droids that controlled them.
The Empire was later discovered by both Republic and Sith forces when Darth Marr led an expedition into the unknown regions. This prompted Valkorion to deploy the Eternal Fleet against them, and Marr as well as an Outlander were brought before Valkorion. However, the Immortal Emperor's son, Arcann, betrayed him and the emperor perished soon after, with Arcann ascending to the throne.
The Eternal Empire quickly became a major galactic superpower, with Darth Vowrawn from the Sith Empire's Dark Council and Senator Evran from the Republic pledging allegiance to it. However, after a series of conflicts involving the Outlander, the Empire's hold on the galaxy began to weaken.
SCORPIO later ascended to the Eternal Throne and used her position to grant the GEMINI droids free will, allowing them to leave the planet.
After being defeated by the Outlander, Arcann went into exile with his mother, Senya. Vaylin later assumed the Eternal Throne after being given it by SCORPIO. Vaylin began using the empire's resources to hunt down Arcann and Senya so she could get revenge on them.