The Story of Apollyon

The beginning of the Second War (which was then considered the first) was a girl named Pandora, who, according to legend, opened a vessel (pythos). Because of this, the Ideas of Evil have escaped the world, as well as all the troubles, diseases, sufferings and vices that have spread throughout the world. Terrified, Pandora slammed the lid shut, but it was too late — there was only Hope left at the bottom. And so began the first war of Heaven and Hell.  The ideas of Evil, led by Abraxas and the creatures of hell, began a war against heaven. Adam, who was creating and repairing creation at that time, noticed this and, gathering his army, went on the attack. This war lasted for several hundred years...

(Adam)

Throughout hundreds of years of Great Conflict, Adam stepped where other angels dared not. When the war benefited the Heavens, he was always the first to lead the most daring attacks in the Burning Hell. When the legions of Hell besieged the Upper Heavens, it was Adam who rallied his fellow angels and was the first to break out of the Pearly Gates to plunge headlong into the disparate armies of Hell. In one of Adam's invasions of Hell with Adam's spear (his spear, forged by him in the heart of a dying star), he defeated so many demons that rivers of blood flowed through the seven spheres of Great Evil.

(Adam leads the fight)
On one of these battlefields, Adam and all the other members of the Supreme Council engaged in battle with their demonic opponents. Adam single-handedly defeated the giant one-eyed demon, and the demons retreated to their fortress. Adam sent the Heavenly host after them. Camael urged caution, but Adam ignored him and entered the fortress himself. Once in its depths, he discovered that his fellow angels were dead, and Abraxas, the Idea of Fear, was waiting for him. They clashed, fighting to the death. Abraxas commented on Adam's rage during the battle, wondering aloud if his angelic enemy was afraid of what other angels would think of him if they saw what he really was. Thus, Abraxas questioned whether "bravery" is nothing more than a manifestation of "rage."

(Adam, on the offensive)

While the war between humans, spirits, angels, and demons raged, Adam eventually got tired of the constant fighting. He decided that the only way to achieve peace was to build walls between the races, hoping that after a thousand years or so they would forget about their enmity. With the help of the Flaming Sword, he erected these walls, sacrificed himself to provide enough magic for this cause.
In the battle with Abraxas and the rest of the Ideas of Evil, the Demon of Fear was able to pierce Adam's chest with the Sword of Sin at the last moment, a sword that manifests sin in a saint and even in a baby. So the first soul was defiled by filth. Seeing his world crumbling, Adam decided to put an end to this long conflict.
If the Sword of Sin caused his sins, then he used the opposite of this sword. He took the Blade of the Patriarchs and pierced himself with it, to the horror of the Heavenly Elders.
As a result, the Power of Hope was released into the world so that mortals could survive the destruction and recover without relying on anyone.

(Adam, uses the first swords to save Creation. This creates a prison where Chaos and Darkness are sealed under seven seals and it is called the Abyss.)

But Adam's soul, which was at the epicenter of all this, could not withstand the load and exploded, scattering into several thousand fragments throughout the universe ...
and so ended the life of the First Man. The father of Mankind died, but two beings of indeterminate power clung to the largest fragment. Fighting with each other to get hold of him, they split him into two equal parts. And the beings who fought for it were the concepts of Good and Evil.

(Good and Evil)

So two new forces were born that must be reckoned with, and one of them is Apollyon...

(Adam, at the end of the conflict and the birth of Apollyon)

(Apollyon is the Angel of Valor and
The Destructive Fury of God)

Other battles
Apollyon was present in the fortress of Pandemonium when Agramon, a demon in the service of Abraxas, led the assault on the fortress. Agramon wore the Noose of Pandemonium, a ring given to him by Abraxas that spread fear among the angels defending the fortress. However, the noose did not affect Apollyon, and he cut off Agramon's hand. Agramon fled the battlefield, and the ring was lost.

Apollyon killed the demon prince Amon, but not before the demon destroyed hundreds of angels.