The Truth is an enigmatic, metaphysical being who appears when a person attempts 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 forceably take their most valued attribute, or something of value that represents their anticipated relationship to the person they are trying to create or resurrect. Truth will accept otherwise impossible exchanges when a Philosopher's Stone is used, as it or part of it will be used for the exchange instead.

As a negative version or "conscience" of the alchemist who performed Human Transmutation, Truth is perceived by the finite human mind as punishing them for "Playing God". As a "God", or "the Universe", Truth embodies the universe, serves as both a deity and Monad for it, and also represents the consciousnesses and consciences of living things. Truth oversees everything in the universe, and regulates all Alchemic exchanges in the world.