Before Kingdom Hearts χ
According to the player's Chirithy, the five Foretellers and one other Keyblade wielder were the apprentices of his creator, the "Master of Masters." Shortly before he disappeared, the Master of Masters assigned his disciples new names and gifted five of them with a tome from the Book of Prophecies, which taught them of the event that would doom the world.
Kingdom Hearts χ
After helping Chirithy fend off the Minute Bombs in Daybreak Town, the Player goes to sleep. They have a dream in which the five Foretellers converse with their master before the Player has a chance to approach the Foretellers and their mysterious visitor, they are engulfed in darkness and wake up. 
Kingdom Hearts III
The Master of Masters is mentioned by the Secret Reports written by Luxu. It was stated that out of the five new Union leaders, there is one he didn't chose. Luxu also lamented that without the Master, the darkness began to spread even without any Keyblade War. It has been stated that the Master will return after the Second Keyblade War comes to a close and the Foretellers are reunited with Luxu, indicating he will appear in the next installations of Kingdom Hearts.
The Master of Masters appears as a person completely concealed in a black coat. Nothing else is known about the Master's appearance beneath the hood, although according to Chirithy he has an eye that gazes into the future.
The true personality of the Master is unknown due to his contradicting manner in all his recent appearances. He constantly behaves in an unpredictable and eccentric manner despite his extraordinary intelligence and wisdom but his ability to stage the Keyblade War while ensuring the worlds would still exist, manipulating his own loyal apprentices with no apparent qualms despite their absolute loyalty and his apparent affection for them, indicates a machievallan personality. His true allegiance remains unknown as although he apparently cared enough for the existence of the worlds to ensure they would survive despite this not stopping him from carrying out his mysterious plans, he was willing to let several disasterous events unfold while merely watching. In addition, he is quite capable of being serious, as displayed by his ability to strike clear worry into his extremely powerful apprentices when they asked him regarding their roles, despite often returning to his old self.
Little is currently known about the Master's skills but as he is the one who trained the incredibly strong and skilled Foretellers, Keyblade Masters themselves, with him still clearly being visibly superior to their level of might, and is regarded by them all with awe. He can casually intimidate even the arrogant and powerful Aced by merely pretending to find his dissaproval of Ira becoming the leader undesirable, hinting he is most likely one of the most, if not, the most powerful and skilled Keyblade Masters around. One of the abilities the Master is known to have is to spawn Keyblades from the hearts of others, which he acquired from studying the X-blade. He also can use his Gazing Eye to see the future and can perceive anything the Eye saw from anywhere throughout time. This ability made the Book of Prophecies he authored possible to exist. He was capable of creating the Spirit Chirithys for the Foretellers and their Union members. He is a brilliant strategist as his actions giving the Foretellers roles to play ensured the Keyblade War would occur. He kept the light from fully expiring, allowing the worlds to exist, but separated, by having the members of the Dandelions transported to a different worldline so as to protect them and their light. This kept the worlds from being completely consumed by the darkness unleashed from the Keyblade War. The Master is implied to share a symbiotic relationship with Kingdom Hearts, as his apprentices believe that summoing Kingdom Hearts would cause his return.
- Main article: The Gazing Eye
Although the main Keyblade of the Master of Masters is unknown, he created and briefly wielded The Gazing Eye, a Keyblade forged from one of his eyes, which he used to see future events in order to write the Book of Prophecies.