The Celestis were the Celestial Intervention Agency, who, during the Second War in Heaven removed themselves from the universe in order to attempt to escape the temporal damage.
Nature
The Celestis removed themselves from history and detached themselves from the physical plane of existence, making themselves ideas, and thus harder to destroy (harder than a physical body tied down to the timeline).
They inhabit a world outside the normal space time called Mictlan, a place that most probably was constructed using the Matrix. It exists outside the physical universe. (EDA: Alien Bodies)
The Celestis were split on whom to support during the War: the Time Lords or The Enemy. (EDA: Alien Bodies) They were known to believe themselves to be gods and were aloof from the Spiral Politic. Due to the nature of their existence, they required people to act on their behalf as well as think of them in order to exist. To do this they often showed themselves to lesser beings in the form of gods. (FP: The Book of the War)
