Long have I awaited this, the day that you would come. A tragedy unfolds now which pains me more than you can know. To end it, I will gift to you my light. Though in so doing, I condemn myself to sorrow greater still.Kluya's Voice on Mount Ordeals.
Kluya, also known as KluYa, is a non-player character in Final Fantasy IV. While he is never seen in the initial releases, only playing a part in Cecil Harvey's backstory, the 3D version greatly expands his backstory in relation to the Blue Planet and thus reveals him for the first time. Kluya is a mage with mystical powers who is also knowledgeable in technology.
Kluya has long indigo hair and beard and blue eyes. He wears a robe similar to that of a White Mage, only the edges are colored indigo instead of the usual red. He wears a necklace with a purple pendant.
Kluya loves his family. He is fascinated with the moon, but tells his son Theodor he will explain about his fascination with the moon when Theodor is older. He wants to pass on his light to Cecil and help him become a paladin. He believes in the industriousness and goodness of others, and when he sees that he can help the people by teaching them his magic and technological skills, Kluya takes up the role of teacher so everyone's livelihoods can be upgraded.
Kluya is a mage of some power, as when he came to the Blue Planet he brought with him the secrets of Lunarian magic, which he taught to the villagers of Mist. He seems to possess some degree of Holy powers, as he was able to, after death, transform Cecil into a Paladin, and later Kain into a Holy Dragoon.
Cid Pollendina was originally credited with the invention of the airship after having deciphered the art of flotation from ancient text (possibly Lunarian in origin), but this was retconned or ignored in the Nintendo DS incarnation where Kluya is the one to have taught technology, including airship building, to Earthlings.
Before the events of Final Fantasy IV
After arriving on the Earth, he sealed the Lunar Whale near the village of Mysidia. Due to his Lunarian heritage making him immortal, Kluya ventured throughout the Blue Planet under different identities in order to avoid suspicion of not being born on the planet. During his travels, he taught mankind how to create new technology, including the ability to build airships and the Devil's Road. Eventually he would also teach humans the concept of magic, which the people would begin to immediately grow more proficient in.
When teaching magics to a small village, he began to fall in love with a human named Cecilia, who was one of his students in magic arts. Due to his feelings for Cecilia, Kluya would remain in the village for ten years, and would reveal his Lunarian heritage to her. Cecilia accepted Kluya despite not being human, and the two left the village together, settling in a small cottage in the forests near Mysidia. As time passed, the two would have their first son, Theodor.
However, despite living happily with his family, Kluya would begin to learn that humans were beginning to use magic for violence and their own selfish means. He would attempt persuade mankind from using magic for such methods, but Kluya's students denounced his words, forcing him to limit his teachings on magic, and also keep his secrets of immortality magics away from the populace. However, despite his pleas and limiting the teachings of the arts, mankind would eventually grow more corrupt and begin to use magics as a means of spreading war, much to his dismay.
One night, Kluya was outside troubled by something and stared at the moon, only to see his son Theodor outside at his side. Theodor noticed that his father loved looking at the moons and asked Kluya why. Kluya simply replied, "I'll tell you when you're older." He told Theodor to go back to bed and then leaned his head down in grief.
The next morning, Kluya's friends and family find him dying outside his home. A villager told Theodor and Cecilia that he was attacked and mortally wounded by a rival faction of villagers who disagreed with his teachings, and intended to use magic to wage war. Theodor attempted to cast Cure, but was unable to do so. However, Kluya's prayers of the Mysidian Legend prevent him from ascending to the afterlife and keep him on the Blue Planet on Mount Ordeals. 
Kluya was alluded to for the first time in Mount Ordeals, although Cecil does not know this yet (Palom and Porom do, however). A mysterious light that appears when Cecil undergoes the trials to become a Paladin calls him "my son". When Cecil arrives on the moon, it becomes apparent he is related to Golbez, as well as them both being related to Fusoya.
Some time after the party defeats Zemus and Zeromus, Kain Highwind trains on Mt. Ordeals and hears Kluya's voice calling to him. Kain enters the mirrored chamber Cecil became a Paladin in, where Kluya tells him he will experience intense pain as Cecil did. Kain's reflection steps from the mirror and attacks him. Kain loses, and the mirrored chamber is shattered as Dark Kain escapes to the outside world.
In Final Fantasy IV: The After Years, when Golbez and Fusoya pray for the Lunar Whale to come to the Red Moon, and Kluya prays with them, the Lunar Whale awakens and flies to them. Seeking answers and preparing for a crisis, the Elder of Mysidia sends Porom to Mt. Ordeals to find Kain and recruit him to defend Mysidia should anything happen. Porom and an escort of mages enter the mirrored chamber to see its damage, and upon leaving they meet Dark Kain, posing as the real Kain. Later, Kain once again confronts his dark side and this time defeats him, accepting his darkness and absorbing him. Kluya recognizes the spirit of justice in Kain and transforms him into a Holy Dragoon in recognition of his trials.
Kluya's fate is unknown—when Porom enters the mirrored chamber, Kluya tells her, somewhat paradoxically, "I... am about to fade... But my spirit...will never be extinguished."
Dissidia 012 Final Fantasy has a trade material called "Kluya's Beard".
- Final Fantasy IV Game Novel Vol. 2. p. 255 - 258