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 machiavellian 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 disastrous 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.
From what has been revealed of his true feelings, he is tired and bitter over having seen the fight with light and darkness go on in an endless cycle, noting that he wants to "take a break" from it and his entire plan of choosing new Union Leaders and ending the current world was all to finally put a stop to the Keyblade War.
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. As the Master has installed one of his eyes inside the Gazing Eye, he has seemingly lost one of his eyes, although it remains unknown if he can't just regenerate or replace it.
Before Kingdom Hearts X
Little is known of the Master of Masters origin; what is known is that, as he said to Luxu, when he was just a boy, the Keyblade War had already began between Light and Darkness and he confirmed that there were other keyblade wielders at that time. Although he doesn't mention if they were his allies or enemies nor does he mention what happened to them, only saying that he is the only one relevant. His words that stated that the darkness took the form similar to but not quite that of a human seemed to indicate he had crossed blades with other Keyblade wielders before, and that despite being a Keyblade Master, he didn't have a Master of his own, seeming to indicate he created the title. He would at one point use his ability to forge keyblades from the hearts of others to take six apprentices, Luxu, Ira, Ava, Invi, Aced and Gula and train them into becoming Keyblade Masters of their own right and also create the Book of Prophecies with his Gazing Eye. Having grew disillusioned with the unending Keyblade War, he decides to end it for once by manipulating his apprentices. First having Luxu tasked with watching over and ensuring the events happen as written in the Book as well as keep the Black Box and it's contents safe and a secret, along with also the additional order to ensure that the Gazing Eye keyblade is passed on to others to relay future events to him and also revealing the truth about his intentions, the Master of Masters then proceeds to make Ira leader of the Foretellers, Aced Ira's right-hand man and Invi the moderator, while he tasks Gula to stop the traitor inside the Lost Page and most importantly, Ava to gather a group of exceptional keyblade wielders from every union to venture out of the destroyed world to ensure the survival of the light and recreation of the world. Finally, he creates the Chirithy to aid keyblade wielders, with a warning to his apprentices that if the wielder falls to darkness, their Chirithy will be corrupted and become a Nightmare, and then vanishes, leaving so little traces that the Foretellers, despite their search, are unable to find the Master.
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. 
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.
Currently, nothing is known about the Master's might but he is certainly an extraordinarily skilled and powerful Keyblade Master, having personally the incredibly strong and skilled Foretellers and Luxu, molding them into powerful Keyblade Masters themselves, while still being superior to their level of might, deemed by Gula as having the power to forcibly stop all of them from causing the Keyblade War. All the Foretellers have shown absolute respect of his strength and even fear of his power, able to effortlessly intimidate even the arrogant and powerful Aced merely pretending to find his dissaproval of Ira becoming the leader undesirable. He is at least strong enough to casually move the heavy Black Box from a kneeling position even without aid from Luxu.
Having extraordinary knowledge, the Master has displayed unique abilities, one which included being able to spawn Keyblades from the hearts of others, which he acquired from studying the X-blade and can also seemingly construct Keyblades of his own without needing to use the hearts of others, as he was able to create the Gazing Eye, which was not his main Keyblade, through unknown means. 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 and placing traps in the flow of time to prevent any attempts to rewrite the past and trapping those who tried inside a data simulation of their world. The Master appears to be capable of sensing whenever Kingdom Hearts is summoned, as his apprentices believe that summoning Kingdom Hearts would cause his return. Through unknown means, he was able to remain alive through the centuries after the Keyblade War with seemingly no deterioration to his vitality and power, indicating he is either immortal or used the same heart-extraction technique Luxu used to remove his heart from his body and then possess another body.
An extremely intelligent and wise man, the Master of Masters is an extraordinary strategist and manipulator, apparently the greatest currently in the entire series, as he gave each of the Foretellers their own roles specifically based on his knowledge of how they would react to successfully ensure the Keyblade War would occur and despite the overwhelming darkness unleashed from the war, he was still able to successfully keep the light from fully expiring and prevent the darkness from completely consuming everything, 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.
Along with that, he also successfully instructed Luxu in how to enact a second Keyblade War that was so magnificently done that Luxu successfully eluded all detection in his part, to the point that even the brilliant Master Xehanort was completely fooled into believing Luxu, as Xigbar, was merely desiring the power of the Keyblade enough to join him.
- 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.
- The Master is shown to very cautious about temporal stability. He doesn't give Luxu a book of prophecy to ensure he doesn't cause paradoxes. He's even boobytrapped time travel to trap those who are attempting to rewrite their pasts inside a digital simulation of their world.