Deus Ex Machina

Deus Ex Machina is the God of Time and Space and a major character in both the Future Diary manga and anime. Co-creator of the Future Diaries alongside John Bacchus, Deus creates the survival game to make sure he has a suitable successor to his title before his inevitable death. Able to manipulate time, space, and the laws of cause and effect, Deus is the most powerful entity in the series and acts as the judge of the survival game.

Appearance
Deus is an extremely large figure, towering over other characters at well over a hundred feet tall. Barely humanoid in appearance, Deus appears as a huge creature made of machinery, possessing a large, skull-like head, sporting spiked purple hair and a crown, and he wears a large dark cloak with ornaments attached.

Personality
Despite being a god, Deus is very playful and laidback, considering most of his actions to be games. Instead of just choosing a successor, he makes the survival game in order to create a more interesting outcome. He seems to be playful to terrifying degrees as he is completely apathetic of the consequences of his games, as seen during his first appearances when he had provoked a war simply for fun. His murderous apathy is also displayed through his creation of the survival game as requires the participants to kill each other via any means possible (assassination, assault, electrocution, poison, slicing throats, hundreds feet falls, explosions, burns, stab, decapitation, bleed to death... any possible way to eliminate other diary owners. Participants can also suicide, if they want, and be eliminated from the game); this is especially sadistic as most of the participants are violently insane, with Yuki, who initially believed him to be his imaginary friend, being the most relatively normal participant. If the participants' Future Diary is destroyed before the game start, Muru Muru will just fix them so there's no way to avoid the survival game unless someone proves to Deus that the game is a bad idea. During the game, however, he's a man of honor and does whatever he believes necessary for the game to be as fair as possible, such as answering questions or appointing/creating a special observer to collect information of the participants. Although far from a benevolent god, Deus is not without compassion and has on few occasions done good things without any personal profit. During the survival game, he saved Minene Uryu from death despite her hatred of him, making Minene a participant despite it being clear that she was not forced to do so, among others. He has also displayed a sense of fairness when he sent Minene on a mission to stop Muru Muru from unfairly supporting Yuno. He even went as far as giving half of his own knowledge and powers to Minene in order to aid her.

Also, the fact that he interacts with few humans seemingly without any explanation implies that Deus may, in fact, be fond of some humans, or at the very least those whom he finds to be interesting.

Powers and Abilities
Deus is an ancient deity who has ruled over time and space and the laws of causality. As god, Deus is very powerful and is able to create and alter causalities through time and space. It is implied that he may be able to rewind time, but leaping back in time can create parallel worlds. Despite being a god, Deus is unable to resurrect the dead. While reviving a body is possible, without a soul, the dead cannot come back to life by any means. Deus has control of the Akashic Records, the universal compendium of knowledge and history. Deus is shown to be able to create artificial lifeforms, namely Aru Akise, revealed to be his "Observer" in the survival game to keep track of the ever-changing futures of the diary owners.

Deus operates from the Cathedral of Causality, depicted as a large domed building colored with a purple tint. Deus sits in a large throne which hovers above the ground. The cathedral also has an arena where the diary owners, Deus and Muru Muru meet for occasional meetings. The arena is covered with an eternal cloudy sky, revealed to actually be a cover for the Akashic Records.

He remains oblivious to the existence of the first alternate world, implying he only has power over the time and space of the universe he lives in. Deus at first makes the choice to not interfere with the events of the game and watches merely as an observer. However, during the second game, when Yukiteru Amano discovers the three corpses in Yuno Gasai's house, the whole pre-planned events of the second survival game are altered, and Deus does not act to restore it, finding the alternate path all the more interesting. He eventually abandons his intention to not influence the events of the game after Muru Muru does. He wishes to make the game as fair as possible, but outside influences force Deus to play his hand near the end of the game to ensure it runs smoothly. He is even willing to abandon the game all together, as seen in the third world when John Bacchus puts a halt to his Future Diary project, canceling out the third survival game.

Deus appears to have extended relationships with the different diary owners. He is rather fond of Yukiteru, at first posing as his imaginary friend and personally makes him the "First" diary owner. Deus openly supports Yukiteru throughout the game, unphased by Yukiteru's mishaps and believes it is all part of Yuki's future to win the game. He also has a unique relationship with Minene Uryu, who does not believe in god and wants nothing more than to rid the world of the very concept of a deity. Minene has a love/hate relationship with Deus, openly hating him but is willing to ask him for advice, and even protests to receiving a portion of his powers when the time comes. Deus views Minene as an ally, using her to put a stop to Muru Muru's plans. Deus and John Bacchus seem to be good friends, creating the Future Diaries together. John seems to care for Deus, but also uses Deus' needs as an excuse to extend his own plans in the survival game, requesting that Yukiteru and Yuno be eliminated from the game to speed it up before Deus dies.

It is never explained why Deus is dying, but his death causes the universe to be swallowed up in black holes. Deus is succeeded three times in the series. In the first world, Yuno becomes his successor, Yuki in the second, and finally Yuki and the third Yuno from the third world.

The First World
Not much is known of Deus during at this except that he was dying as well and started with John Bacchus to choose a successor, and overall oversaw the game from beginning to end without any apparent need to act. It is suggested he died at 28th of July shortly before Yuno won the game.

The Second World
Deus as he appears through most of the series. He's initially shown as Yuki's imaginary friend, and eventually gives him his Random Diary like the other participants received theirs. When Yuki is revealed by Yuno that she possesses a diary, he reveals to Yuki that he never mentioned he was the only one. Following this, Yuki and Yuno face The Third, Takao Hayama and defeat him and immediately Deus invites the remaining participants and explains the Survival Game to them, its rules and the basics of The Future Diaries and call Yuki (by this time The First) as his favourite candidate.

Deus appears expressing amazement towards Yuki who created a large change on the future after he peeps on a secret room on Yuno's house. After this event, Deus keeps overseeing the game until Muru Muru would accelerate things and force The Fourth, Keigo Kurusu into action, which would prompt him to be much more cautious about his servant. He does not take action until the appearance of The Apprentice Users where he invites Yuki (and possibly the other participants) into answering their questions about them.

He appears later when Yuki's mother is killed by his father, and Yuki asks Deus to revive her, to which he says he can't followed by Muru Muru who says he should become God if he wanted things to become normal. He's seen again talking with Muru Muru after Minene's attack on John Bacchus, before feigning about going to rest. Deus is soon visited by Minene in his resting sphere, who asks him about John's Diary. Deus takes this opportunity to transfer some of his powers to her so that she could stop Muru Muru and her scheme to allow Yuno to win the Survival Game, where he suspects that this Muru Muru and Yuno had already won a Survival Game in the First World (Minene's memory of this revelation would be concealed in her mind until much later). Deus also reveals to Minene the nature of John's The Watcher and how he collaborated with John Bacchus to create The Future Diaries.

Following John's death, Deus is, at this point, on the verge of death with the world starting to collapse. Aru Akise visits Deus to confirm if it is possible to bring resurrect the dead. Deus answers that only the body can be brought back, but the soul is an impossible task even for him. Learning the truth Akise tries to warn Yuki, but Deus stops him and reveals to Akise that he's his creation serving as an observer of the game to gather information, and since he has outlived his role he starts to slowly vanish him into the Akashic Records as Akise tries to prove that he has a will of his own. Deus gives him the chance to prove so, but fails and almost destroys him completely until the timely arrival of his own diary - The Detective Diary provided by The Eighth, Kamado Ueshita therefore proving that he was capable of something outside Deus's plans. Amused by this, Deus lets him live on his own account. Deus dies shortly after this, the only thing remaining alive being his core which would last long enough to grant the winner of the Survival Game their prized godhood. In this state, he warns Muru Muru that she must allow the game to run properly as he's restrained by her seals to do so.

The Third World
Deus's core of the second world is given to Yuki after he wins the game, while a third Deus is approached by John who saw his own demise from The Watcher by reading the diaries of the second world's participants who had performed a time leap, to cancel the Future Diary project, therefore nullifying what would be a third survival game. 10,000 years into the future of the second world's timeline, Deus appears with the first and third incarnations of Muru Muru connecting the timelines of the second and third world, along with the Yuno of the third world who was given her first incarnation's memories which practically allowed her first world self to survive. Mostly because Yuki and Yuno have won the previous games and possibly because of convincing from the two Muru Muru's, Deus calls off the game and happily accepts both Yuki and Yuno as his successors, therefore it is implied that he dies at this point or if he's alive, he no longer is the god of time and space.

Trivia

 * Deus is Latin for "God".
 * Deus Ex Machina as a whole is Latin for "God from a Machine" or "God of the Machine". In fiction, it is a term used to name a plot device whereby a seemingly unsolvable problem is suddenly and abruptly solved with the contrived and unexpected intervention of some new event, character, ability, or object. Thus saying "God made it happen," with no further explanation. However, it may be a reference to his machine-like appearance as well.
 * Deus' theme song is "Egoist" by Yousei Teikoku.
 * In the third opening of Future Diary (the one used in Future Diary Redial), Yukiteru can be seen wearing Deus' uniform.