Planet X, a world situated in Wild Space, was the unofficial designation given to a planet. The prospector Radicaz "Sunshine" Dobbs bestowed this moniker upon it, noting its location at the edge of the Galactic Frontier. Marda Ro, the Guide of the Open Hand, following her experience on the planet, preferred to consider it a place without a name.
The Under-Dwellers, beings with a desire to flee Planet X, and the Nameless, predators of Force-sensitives, both called Planet X home. The protector was another inhabitant. Every aspect of this world, including its atmosphere and geology, possessed a form of life and a capacity for self-defense. The Veil, a turbulent and perilous atmospheric layer, served to prevent foreign objects from entering the planet. Passage through the Veil could be achieved through significant loss of life or sacrifice within it, as these casualties would divert the Veil's defenses, allowing others to pass. Consequently, the Ro family believed that accessing the treasures beneath the Veil required a substantial sacrifice.
While the surface of Planet X had restorative qualities, the planet exerted a mental influence on newcomers. This influence induced feelings of euphoria, joy, and rapture, making individuals reluctant to depart and causing them to lose their sense of self unless they actively resisted. Dobbs posited that this was either a defense mechanism to prevent departures or a manifestation of the Force. Even those without Force sensitivity could perceive the Force's flow on this world. Ultimately, prolonged exposure to Planet X could unlock Force sensitivity in visitors, although these abilities could vanish upon leaving.
A kelp-like vegetation covered the rock walls of a cave system, leading to the Under-Dwellers' habitat, which differed from subterranean passages on other planets. During the Path of the Open Hand's mission to Planet X, this vegetation, along with small insect-like creatures, attacked an Under-Dweller attempting to escape. The protector also intervened to restrain the Under-Dweller and subsequently attacked the Path, who were attempting to leave with Nameless eggs. The Veil, too, seemed to expand in an attempt to thwart their escape.
Rumors about the planet's existence circulated around 400 BBY. Around 382 BBY, Radicaz "Sunshine" Dobbs journeyed to the planet with hyperspace prospectors Spence Leffbruk and Dass Leffbruk. During their flight through the planet's atmosphere, Spence and Dass's ship sustained damage. Dobbs offered to assist them in leaving the planet in exchange for half the reward for its discovery. However, Sunshine abandoned them on the planet Gloam. Later, Sky Graf, a scion of the Graf clan, and Dass Leffbruk sought to locate the planet, planning to travel there with Jedi Padawan Rooper Nitani. They were compelled to abandon their attempt when Nitani was summoned to Dalna by her Jedi Master Silandra Sho.
Around the same period, Marda Ro, the Guide, accompanied other members of the Path of the Open Hand to acquire more Nameless for use against the Jedi Order. Calar, a Force-sensitive member, possessed tracking skills that would aid in locating the eggs. His abilities, though rationalized by Bokana Koss, another team member, unsettled Ro and contributed to her growing disillusionment with the Mother's leadership of the cult. During their passage through the Veil, Calar experienced a Force vision revealing the dire consequences of their mission for the galaxy. He implored his fellow Path members to turn back and attempted to destroy the ship to safeguard the galaxy and the Force, but Dobbs killed him before he could succeed.
Upon landing, Bokana Koss and Shea Ganandra developed Force abilities, which concerned Marda, who was already uneasy about Calar's presence. Koss guided the Path to the eggs but then had a vision that revealed their actions would unleash the Under-Dwellers upon the galaxy as a blight, a destructive force foretold by Calar. Koss snapped out of his vision when an Under-Dweller attacked, only to be defeated by the protector. Both the protector and the Veil attempted to prevent the Path's escape with the eggs but failed. However, the Jedi and their allies subsequently defeated the Path in the Night of Sorrow, though Marda survived.
Knowledge of Planet X and the means to traverse the Veil was passed down through the Ro family lineage established by Marda. Sometime between 231 BBY and 230 BBY, Marchion Ro, the Eye of the Nihil—a descendant of Marda's raised to avenge his family—and a group of Nihil devotees known as the She'ar visited the planet to retrieve Nameless specimens. After sacrificing members of the group to the planet's atmospheric veil, Ro successfully navigated it and landed on the planet in the Cloudship Ikoru. Ro then activated an ancient control rod to summon the Nameless, which triggered an attack on him and his group by all of the planet's creatures. Nevertheless, Ro managed to secure several of the creatures and departed the planet with them in the Ikoru.
Planet X was conceived for the Star Wars: The High Republic multimedia initiative and made its debut in the second issue of the 2022 comic series Star Wars: The High Republic: Eye of the Storm by Charles Soule.