Though the Republic and the Jedi cannot aid us, my siblings and cousins, I tell you; we have a duty to protect the outer worlds from those villains who would take advantage of this time of crisis! Together, we shall avenge ourselves upon those evildoers who would lay harm upon the Rimward Systems!
—Carolus Valdayn at the beginning of the Ethereal Intervention in the Outer Rim
Carolus Valdayn was a male Ethereal Human, king of Luctanem, a carrier of the legacy of the then-extinct Astral Defenders, father of the Jedi Lord and Army of Light veteran Hyperius Valdayn and brother of Jedi Knight Adarius Valdayn. Having been born shortly before and grown up during the Republic Dark Age, Valdayn spent much of his reign as king of Luctanem and de facto leader of the Ethereal Demesnes shoring up their defenses and building up forces to launch counterattacks against nearby Sith and other warlords, particularly the Sith lord Oridron Fedicus, better known as Darth Imperius, though he was not the first to bear that name.
In fact, Valdayn became heralded as a hero among the Outer Rim systems which came under Ethereal protection in absence of the otherwise-present Old Republic, thanks to the Ethereal Intervention in the Outer Rim, which he started and led. Having become frustrated by endless attacks by warlords, Sith lords, crime lords, "and who knows what else", he decided to, quote, "do something about it, something they won't recover from". Thus, after nearly three years of preparation, planning and buildup, the Demesne Defense Forces pulled back their defensive posture somewhat, luring invading forces directly into Valdayn's trap.
Soon, Demesnes forces under his leadership were marching triumphantly through the streets of worlds which had been under tyrannical rule for some time in the absence of Republic leadership, and Valdayn personally marched with them. His brother Adarius, and later, his son Hyperius also came along for the campaigns, taking charge of divisions of troops and ships in their own right. However, just as the campaign seemed poised to take even Fedicus' stronghold, effectively securing the south-west Outer Rim against the Sith completely, Valdayn and Fedicus dueled on the battlefields of Trita. As their armies threw themselves upon one another around them, the pair clashed as two titans of war, Valdayn's Force-Sword and Fedicus' lightsaber meeting again and again.
Finally, though, the Sith lord struck a fatal blow, leaving Valdayn mortally wounded on the battle-scarred ground before him. But before Fedicus could either finish him or watch him slowly die, he made a fatal mistake; a villainous monologue. Fedicus leered over Valdayn, mocking him for "failing to defeat" him, for his "pathetic attempt" to protect the Outer Rim Territories, and especially for his "pitiful swordsmanship". At this moment, Valdayn's sword reappeared in his hand, and with his last strength, the king stabbed the Sith directly through the heart, killing him almost instantly with just enough time left for the last words he heard to be Valdayn's voice, saying simply "You talk too much".
Word of his death spread quickly, and the Ethereal Demesnes along with those Outer Rim worlds they now protected mourned his loss as though he were their own father, their own brother, their own son. Valdayn's own brother and son, the latter enraged by his father's death, immediately intensified their campaign's efforts. In time, they linked up with the Army of Light under Jedi Lord Hoth, where the latter joined his forces with the Legions of Light while the former continued the extant Ethereal campaigns in the Outer Rim and, in time, extended them slightly into the Unknown Regions, so as to ensure some immediately-bordering worlds there were also protected.
The famed, heroic legacy of Carolus Valdayn was such that, by the time of the Clone Wars, the members of House Valdayn continued to reverently tell stories of his exploits, his character, his abilities, and perhaps most especially, his reputation for general, all-around "goodness". In fact, across the Ethereal Demesnes and even on some of the Outer Rim and Unknown Regions worlds protected as a result of his efforts, many average people still recalled him as something of a legendary figure, the "great king of the stars", "he who shielded us from darkness", the "man who brought salvation", the "greatest of all the great Valdayns", and countless other such epithets. Even as late as the Second Imperial Civil War, lord Zaedus Valdayn once remarked that he hadn't "heard of someone so brave since my grandfather told me the story of Carolus (Valdayn)!".