The Proemial Gods were the first sentient beings in the Marvel 616 universe, along with Galactus. Each of them were tasked with specific aspects of the infant universe in order to help it nurture and grow. Eventually, the one known as Diableri, who was the aspect of chaos, convinced his fellow gods to discard their responsibilities and a fight between the Proemial Gods broke out, eventually bringing Galactus into the fray. Only two of these entities appeared to have survived the confrontation, but were imprisoned by Galactus in the prison known as the Kyln, where only the most dangerous life forms in the universe are kept locked away.
During the Annihilation Wave's invasion of the positive matter universe, the Kyln was destroyed, freeing the two trapped Proemial Gods known as Aegis and Tenebrous. They sought revenge upon Galactus and managed to defeat him and his herald, the Silver Surfer. After this, they remained away from the conflict that stemmed from Annihilus' campaign. Eventually, the Silver Surfer caught up to them and seemingly destroyed them by riding the wave of energy at the edge of the known universe and spilling it onto them.
However, the two would reappear and fight alongside Galactus and other cosmic entities when the Fault, a rip in time and space, opened up to reveal another universe that had been taken over by cosmic horrors known as the Many-Angled Ones. Aegis was killed during the battle and Tenebrous' whereabouts are currently unknown.