Agron originates from a distant possible future of the final days of Earth, when both the moon and the sun (then a red giant) are about to collide with the planet. In this future, life has evolved into formless mental energy with great powers. It is uncertain how many other energy beings exist on that Earth, or whether they all possess Agron's level of power.
Fearing the imminent destruction of his world, Agron fled into his past, to the modern era, where it found and inhabited a human corpse in a mortuary. It left the mortuary and embarked on a rampage until it was captured by SHIELD I. However, it gradually increased its control over its powers and escaped its containment cell. Agron feared that it would either be destroyed or sent back to its future to die, so it naturally went on a rampage and attacked or destroyed everyone and everything in its path. Agron overpowered the Falcon, and a number of SHIELD agents. Captain America was also unable to stop Agron's rampage. However, SHIELD agents brought forth a containment tube, and Captain America and the Falcon were able to anger Agron sufficiently to decide to abandon its physical form to attack them with its full force. The Falcon duped Agron into chasing him, and fled through the containment tube, where the SHIELD agents trapped Agron.