The Truth

Truth, or "God" is an intangible being who exists in the Fullmetal Alchemist universe. Truth oversees everything in the universe, and regulates all Alchemic exchanges in the world. Truth reveals himself when alchemists attempt to "Play God" through attempting Human Transmutation. Seeing Human Transmutation as an unfair exchange according to the equivalent exchange laws of Alchemy, Truth will bring the alchemist into the Gate and take something of value that represents the relationship of the person of whom the alchemist is trying to bring to life. The only way to override the power of god is with the legendary object called a Philosopher's Stone.

Appearance
Truth appears as a pure white, nearly formless being almost indistinguishable from the rest of the endless white expanse which surrounds the Gate but for a shadowy outline which causes Truth to reflect the shape of the person it is talking to, thereby supporting its claim to be another shade of that very person. When Edward and Alphonse Elric each appeared before the Gate, Truth took on the shape of a young boy and when Izumi Curtis appeared, Truth's shape reflected that of a young woman. It appeared as a vigorous man to Roy Mustang, and when Father entered the Gate, he apeared as a white version of Father's original form.

Purpose in the Series
Truth initially introduces itself as the being some people call God, the World or the Universe, at first seeming welcoming and jovial to its guests before calling attention to their hubris and opening the Gate, which forces them inside. Truth seemingly has no sense of conscience, as his only objective is to uphold the laws of equivalent exchange, without regard of how he upholds this law. His sense of payment is often based on cruel irony. Due to Edward Elric opening the gate in an attempt to bring his mother back through human transmutation, Truth is responsible for the taking of Edward's left leg and his brother Alphonse. In this case, the irony was that Edward had to pay the leg he stood on and the only family he recognized as having left. Edward paid his right arm to get Alphonse's soul back, which Truth recognized as an equivalent exchange. Izumi Curtis attempted to bring back her stillborn child through human transmutation, and Truth took some of her internal organs, leaving her incapable of ever becoming pregnant again. An unusual case is Roy Mustang, who was forced to open the gate by Wrath and Pride. Regardless of this conscious decision to not perform human transmutation, Truth still punished him by taking his eyesight. The irony was that he saw a promising future for Amestris if he were to become Fürher. It would appear that Truth's goal is to discourage humans from treading in God's domain, as it calls Edward a fool when the young boy returns and sacrifices his arm to recover his brother's soul.

Though Truth appears in Edward's dreams, mocking him, his next true appearance is in Chapter 53, when Edward crosses to the true Gate from inside Gluttony's internal imitation. Truth appears amused that Edward has not come to retrieve anything that he lost on that day four years ago. Interestingly, Truth does not seem to appear before Edward as he discovers Alphonse's Gate and the body that sits before it, but - as the body speaks to him even while its soul is in the mortal plane - it is likely that what Edward sees and speaks to is Truth wearing Alphonse's body just as it wore Ed's limbs, especially since the body is seated in the same manner as Truth whenever it appears.

In Chapter 102, Father discusses the irony behind the works of the 'Truth', who took Ed's way to 'stand by himself' and his 'only family', Al's body so he 'cannot feel the mother's warmth as he craved', Izumi's 'capacity to nurture the seed of life' and, now, with Mustang, coming full circle, 'depriving the man who had a grand vision to save his country of his eyesight, denying him to see what his beloved nation will become'. In Chapter 107, Truth appears once more before Alphonse once his body and soul are finally reunited. It returns Edward's arm in exchange for Alphonse's soul, and mockingly questions the younger Elric if his brother will return for him and what he'll sacrifice.

In Chapter 108, Truth appears before Father and mocks him for trying to claim the power of God for himself. He then banishes Father to depths of the Gate, where he had presumably come from. Truth also appears before Ed and asks what he'll give up in order to bring back Alphonse. Edward confidently marches to the Gate and declares the loss of his alchemic powers as his toll. Truth seems a little startled by this and asks if Ed will be all right without alchemy. When Ed says he will because he still has his friends, Truth gives him a friendly smile, declaring Ed's victory over him, and fades away along with Ed's gate, rendering Ed unable to use alchemic powers for the rest of his life.

Trivia

 * The Truth appeared in an extra in volume 18 of the manga where it showed Yoki attempting human transmutation and having his hair taken as a toll.
 * In a late interview with the author, Arakawa said the Truth was somewhat a 'hollow' version of oneself (as a sort of 'internal God', or conscience), a sort of 'negative' of that alchemist, which completed itself with the tolls taken by the alchemist upon seeing the Truth.
 * The Truth shares the same English voice actress as the 2003 anime's version of Wrath, who was also responsible for taking Ed's limbs in that series. In the Japanese version, however, Truth takes on the voice of whoever encounters him with a slight effect added to differentiate, which is more in line to its role as a literal 'part' of whomever it is engaging with.
 * In the English dub, when Ed offers up his alchemy to Truth in order to bring Al back, Truth takes on a legion-like crossover of Ed and Al's voices in its shout of approval in a similar vein to the Japanese version, likely for emphasis of the scene.
 * For some reason, in the 5th Fullmetal Alchemist: Brotherhood Opening "Rain", Winry appears as Truth.
 * The ethereal being of Truth can be connected to the teachings of Theosophy (see Gate Trivia for connection between the Gate and Theosophy) where in Theosophists believe that "religion, philosophy, science, the arts, commerce, philanthropy and among other virtues, lead people closer to "the Absolute". Planets, solar systems, galaxies, and the cosmos itself are regarded as conscious entities, fulfilling their own evolutionary paths. The spiritual units of consciousness in the Universe are the Monads, which may manifest as angels, human beings, or in various other forms. According to Blavatsky, the Monad is the reincarnating unit of the human soul, consisting of the highest of the seven constituent parts of the human soul. All beings, regardless of stature and complexity, are informed by such a Monad." From this, we can assume that, if Hiromu Arakawa intended the gate of truth to be connected to the teachings of Theosophy, then the Truth would be the Monad.
 * This can be justified by the motto of Theosophy, which is "There is no religion higher than Truth". The emblem of Theosophy also depicts the Ouroboros in it; the Homunculi are a reference to this, as they are the children of Father, who by extension came from Truth itself.
 * It is also interesting to note that, in the same topic of Theosophy, they teach of the root races of humanity (of which we are in the fifth, the Aryan race,) where they teach that the Aryans established "The City of the Bridge", which is said to be below the city called Shamballa. This could be where the first theatrical film idea "Conquer of Shamballa" came from. This could also be interconnected with the Theosophic ideas of The Gate of Truth, as Dietlinde Eckhart had to pass through the Gate in the 2005 film in order to get to the supposed Shamballa that was Amestris.