The Dark Begins To Rise...

In 18,000 B.C. during the arrival of The Second Celestial Host, Arishem judged The Deviants unworthy to rule the Earth and proceeded to wipe them out along with his fellow Celestials with the exception of a golden celestial named Tiamut the Communicator, who had need of The Deviants services. Tiamut stood against his brothers and clashed with them both on Earth and in space.
 
But Tiamut proved to be more than a match for the combined power of The Second Host and nearly achieved victory when his former brethren unleashed a weapon capable of crippling a Celestial long enough for them to be subdued. Once Tiamut, whose armor changed from gold to black after being hit, was down, Arishem and the others sealed him away beneath the Diablo Mountain Range in California. Afterwards, Tiamut's true name was stricken from history.
 
Several millennia later, the world-devourer called Galactus was subjected to the power of the Images of Ikkon spell and had the cosmic equivalent of a stroke. Galactus' fall roused 'The Black Celestial' from his 'slumber' and he used what little of his power he was able to tap into to take control of Galactus and turn him into a weapon powerful enough to devour the Universe.
 

Thanks to the machinations of his Deviant followers, the Black Celestial was able to escape his prison, though he emerged greatly weakened. Thankfully, The Deviants had built a machine in the base they constructed around his body within the mountains that would constantly transfer immense amounts of energy into their master's body until he could regain his former strength.
 
The Black Celestial later intercepted the entire Shi'ar Amada, who sought to destroy the now greatly enlarged Galactus, who was devouring everything via the use of his energy conversion machines and an artificial black hole created by the Black Celestial to speed up the universe's death. 
 
Before the Shi'ar could even grasp their minds around the concept of Galactus being a pawn in some major conspiracy crafted by a Celestial seeking to destroy everything, the Black Celestial teleported them into the black hole and fed their life energies to Galactus, much to the horror of Earth-616's Thor, Iron Man and Fantastic Four, who had ended up in his reality by accident. 
 
With the Shi'ar out of the way, the Black Celestial turned his attention towards his mighty "Galactus Engine", not realizing that another Shi'ar vessel commanded by Gladiator of The Shi'ar Imperial Guard had appeared in the vicinity. It wasn't until Earth-616's Reed Richards threatened to travel back in time and warn Arishem and the others of this catastrophe, that the Black Celestial's attention was drawn to the lesser lifeforms.
 

The Black Celestial, now filled to bursting with rage, followed them into the timestream using a great deal of his power, unaware that he was burning away his last power reserves thanks to Gladiator's sacrifice and the destruction of the Black Celestial's base.
 
Through time and space they raced until finally they all returned to the present where the 616 heroes dove straight for the black hole and moved out of the way just in time. Unfortunately, with his power reserves almost completely drained, the Black Celestial was unable to move out of the way and was absorbed into Galactus, killing him in the process.