The Horizon Guard were an elite group of warriors strong with the Force, established by Eternal Empress Vaylin after she took the throne. Empress Vaylin personally selected the members of the Horizon Guard from the existing Knights of Zakuul. Their primary duty was to serve as the Empress's personal protectors.
Following her ascension to the throne, Empress Vaylin of the Eternal Empire established the Horizon Guard, an elite fighting force composed of warriors sensitive to the Force. The Empress handpicked these warriors from the ranks of the Knights of Zakuul. The Horizon Guard served as Vaylin's personal guard and also commanded various field operations.
After the Commander of the Alliance defeated Emperor Arcann in 3630 BBY, his sister Vaylin, then known as High Justice, seized control of the Eternal Empire and claimed the throne. One of her first actions was to eliminate the Zakuul Knights responsible for the Emperor's safety. Subsequently, she formed the Horizon Guard, an elite unit chosen from the remaining Knights of Zakuul. Due to the likelihood of incurring Vaylin's unpredictable wrath, the Horizon Guards adopted the unofficial motto: "I serve for life, but I don't serve for long."
During the invasion of Voss in 3630 BBY, Empress Vaylin, directing operations from the Spire on Zakuul, dispatched several Horizon Guards to spearhead the attack and provide progress reports. During this invasion, Horizon Guards and skytroopers attacked the Tower of Prophecy, which served as an improvised command center for the Alliance. However, they were defeated by the Alliance Commander and their companions. Later, Horizon Guards accompanied Empress Vaylin and SCORPIO on a mission to infiltrate and seize the Gravestone. After successfully capturing the ship and its crew, Koth Vortena, the captain of the ship, contacted the Alliance for help. Alliance forces arrived to rescue the vessel, and the Commander infiltrated the ship to meet with Koth Vortena. During their attempt to regain control of the ship, two Horizon Guards, Tragus Rova and Vella Zarkot, intercepted them, intending to capture them and deliver them to Vaylin. However, the Outlander defeated both of them.
During the Grand Festival of Empress Vaylin, Horizon Guards were assigned to protect key locations within the Palace of the Eternal Dragon. When Arcann and his loyalists, along with the Commander, Theron Shan, and Zakuulan insurgents, launched a surprise attack during the festival to stop Vaylin, the Horizon Guards engaged the invaders while the Empress attempted to escape the palace. After reaching her personal flagship, Vaylin fled to Nathema, hoping to remove the mental conditioning that restricted her full potential with the Force. Once on Nathema, she took several Guards with her to the surface, ordering them to guard the entrance to the Sanitarium. Shortly after Vaylin's arrival, the Alliance Commander and Lana Beniko killed the Guards while attempting to prevent Vaylin from breaking her mental conditioning.
After successfully breaking free from her mental conditioning, Vaylin launched an attack on Odessen. Numerous Horizon Guards, including Imperator Sunfell, participated in the assault, providing support on the front lines. Another contingent escorted Vaylin and her prisoner to the Alliance base, where she confronted the Commander, ultimately leading to the deaths of the Guards and Vaylin.
Following the collapse of the Eternal Empire, the remaining Guards dispersed throughout the galaxy. Former Horizon Guard Scout Captain Sterla collaborated with Battalion Commander Tassar to construct a new Star Fortress on Rakata Prime, but their plans were thwarted by the Eternal Alliance's forces. In 3629 BBY, another former Horizon Guard, Vinn Atrius, initiated a campaign with the goal of destroying the Alliance using Zildrog, an ancient superweapon from Iokath. Atrius established a base of operations at an abandoned listening post and sought allies to join his secret Order of Zildrog. However, in 3628 BBY, Theron Shan infiltrated the order, enabling the Commander to locate and capture Atrius on Nathema, thus ending his plans.
In 3626 BBY, the Alliance Commander, Kira Carsen, and Scourge boarded a ship transporting Satele Shan and her students, who had been rendered unconscious by Tenebrae's curse. The three entered Satele Shan's mind, where Tenebrae resided. Before Tenebrae's demise, the spirits of those he had manipulated over the centuries appeared before him. Among the multitude that joined the Commander in defeating the Sith Emperor were several Horizon Guards.
The Horizon Guards favored lightsaber pikes and lightsabers as their weapons. They typically wore black and gray armor, although a white variant was also known to exist.