Regis Lucis Caelum is the one hundred and thirteen King of Lucis, the son of Mors Lucis Caelum and Alena Andrea, father of the True King Noctis Lucis Caelum, wife of Aulea, and father-in law of Lunafreya Nox Fleuret.
Known to have been the greatest king in Lucis history, Regis ascended to the throne after his father died and fought Nifleheim's tyranny in a large war and nearly won. Having maintained the Wall for so long he has been weakened, Regis is left by no choice but to fool Nifleheim into believing he was tricked by their truce so as to make sure he can deal a major blow to Nifleheim. Having been aware of his son's fate and his death being neccessary, Regis valiantly faces his fate but his sacrifice heavily cripples Nifleheim, as he removes the Ring and asks his predeccesors to grant him fully all his peak prowess for the sake of all of Eos, which allows him to destroy about every soldier sent to Lucis and kill the Supreme Commander Glaucea, who was revealed to be a former Kingsglaive of his. While he passed away, Regis died a heroic death and peacefully rests in the afterlife. He will forever be known as the Honorable Father of the King of the Dawn of Lucis.
Known to be a wise, benevolent and noble king, Regis fully understands what it means to be a King. He has full mastery of the ways a royal interacts and he treats his subjects as equals. Regis cares deeply for his son Noctis and is distraught by the fate he will inevitably face. Although he is not especially fond of Noctis being the true king either as it also means Noctis will die too, he finds solace in how his sacrifice will allow his son to be the greatest king in the history of all Lucis and Noctis's death to be a far more glorious and heroic end. His son's safety is his number one priority and he ensures several means to make sure Noctis fulfills his destiny. He was unable to watch as Noctis is attacked by the other Kings of Lucis and hesitates for a while to deliver the final blow until Noctis reminds Regis on how he is ready, at which Regis sadly smiles and stabs his son with the Sword of the Father. Due to knowing what Noctis will face, Regis ensures as happy and normal of a childhood as possible for Noctis. Despite having loved his wife and been devastated by her death, he was able to remain a fully capable king until the end for not only the sake of Lucis but also for his son. He believes that Noctis must forge his own path to his destiny and encourages him to never lose his way and stay and walk tall no matter what happens. Regis trusts Ignis, Prompto and Gladio greatly to the point of always believing correctly that they will be with Noctis no matter what and he advises them to let Noctis decide his own path. A selfless man to every core of his being, Regis calmly and bravely faces his death. All the Lucian Kings held him in such a high regard they quickly agreed to grant him his wish of having his peak restored for he is not doing it out of greed but out of a desire to protect the future. Regis never relents in his final battle, showing no fear at the massive amount of numbers and weapons wielded by Niffleheim. However, he shows compassion for Glaucea's feelings and after he triumphs over him, he tells him to rest in peace as his past will pave way to the future via Nyx. He does not resent his traitorous Glaive and calmly shares his secrets and even honors Glaucea for retaining honor despite all his twistness. He shows similiar empathy for Ravus, sparing him as he feels guilty on how his abandonment of Ravus and Luna made Ravus the man he is today. As he dies, Regis remains calm and happy to the end, taking his wife's hand lovingly as they ascend to the afterlive.
Regis is an extremely intelligent and wise man, known for having excelled greatly in his studies and possessing sight beyond most of his age while only a child. As an adult, he is an exceptional leader and strategist capable of leading Lucis with effiency unrivaled by any other king before him and having been on the verge of winning against Niffleheim despite the Emperor's own great intelligence and having been able to land a critical blow on Niffleheim at the cost of his own life, machievalanly tricking the Emperor completely into believing he was tricked by his plans while in actuality it was Regis who was utterly deceiving him as he had knew from the beginning the truce was false. His sight is shown by how he is not fooled by Glaucea's seeming return to the Glaives and also having the sight to tell Ignis, Prompto and Gladio were the highest-ranking potential friends of Noctis as well as deducing Gladio would be Noctis's best friend. He is so charismatic that all of Lucis and the kingdom's allies are loyal to him, with King Alfred later noting Regis had been a "charismatic blighter", and they retain their loyalty after his death to the point they unquestionably followed Noctis just due to Regis ordering them too. Regis is also an exceptional tactician, capable of quickly devising methods to fight the overwhelming force of Niffleheim while in a pinch and eventually winning his last stand.
Regis's prowess in battle is immense. Having participated in and won dueling tournaments during his childhood without using his powers in all sorts of combat, Regis was known for being a very gifted boy and would develop his abilities rapidly to the point of engaging in and surviving battles unscathed while not even an adult. At his prime, he could overpower and destroy Ardyn's body despite his ancestor's millenia worth of experience and the latter being stronger a bit than when he faced Noctis; Ardyn describes Regis as being more skilled than Noctis as the True King until he and Ardyn reached the Otherside of Eos, although this was partially due to Regis's strong will and determination to protect his son and Ardyn's true self struggling against his darkness. An extremely accomplished swordsman, Regis primarily uses the Sword of the Father with great skill, unleashing many powerful combos and being capable of easily killing many Nifleheim forces and large monsters in his youth, and despite his aging body, enough has remained of his prowess with the sword that he can fight reasonably well against Glaucia, impressing the general and landing an injury before being overpowered, and despite being wounded from the battle, overpower several soldiers of Niffleheim. While restored to his peak, although he noted he was not quite as strong as he is in his prime but closely, Regis's combat abilities was able to decisively defeat the general, overpower and kill every single one of Niffleheim's forces, and despite having been exhausted and injured, could still defeat Glaucia. He made use of firearms (also using them as improvised blunt weapons) and hand-to-hand combat during his decimation and displayed great skill, easily disarming several Niffleheim soldiers and taking their gun before casually shooting down several soldiers and used at 2 occasions the guns to expertly defeat several sword-wielding Niffleheim soldiers. He was also able to wield the Bow of the Clever expertly, shooting several guns to cause explosions and outright out-shooting Niffleheim soldiers all from a great distance with ease. At one point, he wielded both the Sword of the Father and Blade of the Mystic skillfully, deflecting over thousands of bullets back at without a single one hitting. Wielding the Ring of Lucii, Regis wields magic of immense power and he wields greater mastery and strength over the magics than any other king before him. He is powerful enough to have maintained the Wall for decades, lasting much longer than any King before him and retaining a decent amount of strength. Even while elderly, he can cast powerful holy, thunder, ice, and fire spells capable of killing several soldiers of Nifleheim with one shot, generate durable protective shields capable of blocking attacks from the likes of Glaucia and is still fully capable of conjuring weapons from thin air. At his peak, Regis wields all the highest levels of elemancy spells and can manipulate the Old Wall. His prime has even more magical ability, allowing him to use spells such as Flare, Starfall, and he can cast powerful debuffing and healing spells. While his older age has prevented him from warping and phasing too much, once Regis regains his peak conditioning, he can teleport around at even greater speed than his still younger son Noctis. Regis's overall might at it's fullest is surpassed only by Ardyn and Noctis at their fullest true powers and rivaled only by his ancestor Somnus.
A scholar in the arcene ways of Lucis, Regis was known to be extremely knowledgeable in the art from his decades of research on the lore. He was the only one apart from Somnus who discovered the ancient spell to bestow a portion of the king's powers upon others and also how to craft elemancy spells, all which he taught to Noctis.