“In a time when the Living Universe was young, and it was full of chaos. There was beauty, but it was the beauty of the void, formless and without intent. The cosmic Consonance deemed that there be order and balance to this chaos. The universe does not measure time, but by natural sequence, a balance was struck and the cosmic consonance was set. From the chaos came order, and from order intent. They were the care takers, conceived through intent. Each of them was tasked to maintain the cosmic consonance. They were without will and without awareness of anything but the task set before them. They existed to serve the living Universe. They were the Proemial Gods.
The Gods shepherded the young Universe, maintaining the delicate balance between order and chaos. As a result the Living Universe expanded and flourished. Life thrived on countless worlds, each life form unique from the other. They were formed by the choices made and action taken, by those serving the cosmic consonance. The better they performed their task, the less they were needed to perform their assigned task. The Living Universes' need for them lessened, and the Proemial Gods started diminishing from existences. One of their members, whose functions evolved into awareness and that awareness, had become dark ambition. Diableri of chaos would not see himself erased from the Living Universe. So he embarked on a mission to remake the Universe in his own image.
For his new found purpose Diableri corrupted the purpose of the Proemial Gods, many of them came to embrace his dark ambitions; those most loyal to him were Aegis and Tenebrous. The Proemial beings became engaged in a War of Gods, and Gods died. Had Diableri not brought his war to Galactus he would have achieved his dark ambitions.”
Taken from the Marvel Universe Wiki
Proemials were non corporeal forces of nature that appeared at the beginning of the universe whose task was to prepare what existed for what was to come, by maintaining balance between order and chaos and eliminating early elements they deemed unstable.
As the universe stabilized and corporeal life started to develop, most disappeared but some developed awareness and sentience. As such they developed shapes, identities and even genders. Lead by Diableri of Chaos, one of them that evolved into the embodiment of entropy, decided to reshape the universe so it would suit them better. They fought the World Devourer Galactus and were vainquished. Tenebrous of the Darkness and Aegis, Lady of All Sorrows were among the only remaining survivors of that brutal battle. Galactus imprisoned them in the prison planetoid known as the Kyln, located in the Crunch Cascade a sector of space outside the Local Group known as the. They remained locked in there for eaons until 2007 when they were freed by the destruction of the Kyln during the Annihilation Wave, an invasion attempt by a communal insectoid species from another dimension.
Once free, Tenebrous and Aegis confronted Galactus and his newly restored Herald the Silver Surfer in battle and easily defeated them. Leaving them to be stripped of the Power Cosmic by the forces of the Annihilation Wave, Tenebrous and Aegis returned to the ruins of the Kyln to look for the other Proemial Gods which could have also been prisoners there. To their disappointment, they only found the fallen body of Antiphon the Overseer who had apparently fell victim to the destruction of the Kyln. The Silver Surfer who had escaped captivity tracked down the two Gods and defeated them by using the powers of the Crunch.
Source: Marvel Universe, “Annihilation” Marvel Universe Wiki