Fallen One is Galactus' first herald and was made with the power to control dark matter, as opposed to later heralds that he imbued with his own Power Cosmic instead, since the dark matter is what drove Fallen One mad in the first place. Galactus can manipulate any energy or matter on large scales, and dark energy and dark matter are simply different forms that Galactus is capable of manipulating.

Dark Matter/Energy and the Power Cosmic are both unlimited power sources, but the Fallen One actually has access to that unlimited source, where heralds that have the PC cannot access the full potential of all the PC, as Galactus can control how much he gives them. It would seem to be a precaution on his part.

@Amazingoctus: The Fallen One's true origin is unrevealed as of yet. Dark matter is just another piece of the universe and exists in our universe as well, making up most of the universe. It is hard to detect as we cannot view it directly. Since it is so abundant in the universe, the Fallen One has a virtually inexhaustible source of power. Although he still pales in comparison to Galactus, he is obviously able to put up enough of a fight against his master to change how he empowers his heralds.

The Power Cosmic (totally fictional) is a power source that originates in the Astral Plane and seems to be directly linked to Galactus. Galactus true form is energy and he made his armor to contain himself. I assume the energy he is made of is the Power Cosmic itself, but I don't believe this has ever been stated directly.

 Yeah Powercosmic is fantasy but dark matter seems to be based on what might be scientific reality - cos scientists haven't totally confirmed proof of Dark Matter
 
The wiki Entry on Dark Matter   
  http://en.wikipedia.org/wiki/Dark_matter

In astronomy and cosmology, dark matter is matter that is inferred to exist from gravitational effects on visible matter and gravitational lensing of background radiation, but that neither emits nor scatters light or other electromagnetic radiation (and so cannot be directly detected via optical or radio astronomy).[1] Its existence was hypothesized to account for discrepancies between calculations of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and calculations based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic medium.According to observations of structures larger than solar systems, as well as Big Bang cosmology interpreted under the Friedmann equations and the FLRW metric, dark matter accounts for 23% of the mass-energy density of the observable universe. In comparison, ordinary matter accounts for only 4.6% of the mass-energy density of the observable universe, with the remainder being attributable to dark energy.[2][3] From these figures, dark matter constitutes 83%, (23/(23+4.6)), of the matter in the universe, whereas ordinary matter makes up only 17%.Dark matter was postulated by Fritz Zwicky in 1934 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe; these observations include the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.Dark matter plays a central role in state-of-the-art modeling of structure formation and galaxy evolution, and has measurable effects on the anisotropies observed in the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation. The largest part of dark matter, which does not interact with electromagnetic radiation, is not only "dark" but also, by definition, utterly transparent.

 
 
 

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