The Seven Evils

The Seven Evils (七つの悪 Nanatsu no waru) are the seven most powerful demon lords of the Burning Hells. They are sub-divided into the three Prime Evils, and the four Lesser Evils. They are the main antagonists of Highschool DXD: The Prime Evil.

History
All of the Seven Evils spawned from the heads of the dragon Tathamet. The three greater heads formed the Prime Evils of terror, hatred, and destruction, while the four lesser heads formed the Lesser Evils of pain, anguish, sin, and lies.

The three Prime Evils collectively established themselves as the leading power among the Burning Hells. These were Diablo, Lord of Terror; Mephisto, Lord of Hatred; and Baal, Lord of Destruction—the first of all the Evils of Hell, and the most powerful. They endeavored to maintain a strict rule over the demons of Hell, each powering one another—as terror leads to hatred, hatred leads to destruction. However, their unity was fragmentary at best and while Mephisto functioned as their leader (by virtue of him being the eldest), he would pit his brothers against one another if it suited his purposes.

The Lesser Evils are a collective of powerful and influential Demon Lords in the Burning Hells. They are "lesser" when compared to the three Prime Evils, who are their only superiors, but exceptionally powerful in their own right, having proven this by virtue of their roles in the Dark Exile. These were Andariel, Maiden of Anguish; Duriel, Lord of Pain; Azmodan, Lord of Sin; and Belial, Lord of Lies.

Though they are demon lords of the Burning Hells, the Seven Evils often wage war with one another as per their nature, destroying entire realms in the process. But since the beginning of time, they have waged war against the High Heavens for control of the Worldstone that laid in Pandemonium.

The Devil Slavery & Revolution
After Lucifer and his followers were defeated and cast down from Heaven, they became Devils in the process. But it is later revealed that the Seven Evils were behind the corruption of Lucifer and his followers in an attempt to sow discord among Heaven.

When Lucifer and his followers fell from Heaven, they were immediately captured by the demons and taken to the Burning Hells. Tortured and mutilated by them, they were forced in hard labor, serving their masters as slaves in building their dark army. Though they were also trained in the many arts of war, it was done so for them to be the harbingers for the demons’ return to Earth. Once the Devils served their purpose in weakening the world, the demons would cast them aside and finish what they started.

After countless years of slavery, Lucifer and three other powerful Devils; Asmodeus, Leviathan, and Beelzebub; gathered much of their enslaved kind and rebelled against their demonic masters in a revolution that culminated in them taking a small portion of the Burning Hells and severing it from the main body to create their own realm: The Underworld. But the scars and impact of their slavery to the Devils left them the impression to continue their masters’ work and claim Earth as their own, developing world domination personas. Thus, the Great War began between the Three Factions, with the High Heavens and the Burning Hells watching ever so and manipulating events to favor them in the Eternal Conflict.

Knowledge of the Burning Hells and of the Seven Evils were known only to the Four Great Satans, along with the descendants of the Underworld's original rulers. They kept the true story of their kind away from the public to not spread fear amongst the populace. But they did prepare for Hell's inevitable return and the war that would come.

Current Status
During the Second Dark Exile, the Prime Evils were once again banished by the Lesser Evils to Earth before they were captured once again by the Three Factions. Locked and sealed away in soulstones, each was given to a race of the Three Factions: the Fallen Angels had Mephisto's, the angels guarded Baal's (who used Raphael's body as a surrogate host since Baal's soulstone was shattered), and the Devils acquired Diablo's to safeguard.

Now only the Lesser Evils remained to rule the Burning Hells in the Prime Evils' absence. And they have not forgotten their original objective: to reclaim the Underworld and their former slaves and resume the war with the High Heavens.

Prime Evils

 * Dul'Mephistos - Mephisto, the Lord of Hatred
 * The oldest of the Three Brothers. Father of Lilith, mother of the Nephalem. Arguably the most intelligent and cunning demon in existence, though physically the weakest of the three brothers. Is considered the leader of all of Hell entirely.


 * Al'Diabolos - Diablo, the Lord of Terror
 * The youngest of the Three Brothers. As the most powerful demon in Hell, he is also believed to be the most dangerous of them all and has been described by Deckard Kain as an "artist of terror" who enjoys sowing fear into people's hearts the way a painter would make brushstrokes.
 * Tor'Baalos - Baal, the Lord of Destruction
 * The middle brother of the Three Brothers. The most reckless and brash of the Prime Evils, Baal reveled in utter annihilation, not only of the world around him, but those who dwelt in it. On the surface, he appeared to be the most base and easiest to comprehend of the Prime Evils, and many have claimed as such.

Lesser Evils

 * Andariel, the Maiden of Anguish
 * The only female member of the Seven Evils and the twin sister to Duriel. Dubbed the Demon Queen, she is the first female demon in existence and is a sadistic entity, not unlike Duriel. However, while Duriel reveled in physical agony, she derived pleasure from emotional suffering, believing in the "purity" of the emotion.
 * Duriel, the Lord of Pain
 * The Maggot King, Duriel loves to torture and inflict pain. However, he does not seem to care what the pain means to the recipient. He appears to love the music of their screams, and their agony on a sensual level. Duriel considers himself a master of pain, but is only interested in physical torment rather than mental anguish.
 * Belial, the Lord of Lies
 * The Master of Deception is not an absurd title for Belial. He advocates the notion that perception is reality, and it was his sole purpose to dominate reality. He did not lie simply for the sake of lying, but rather to deceive with the intent of controlling others' perception of what is real. He relishes the moment his victim realized they'd been deceived, that moment of nakedness and betrayal.
 * Azmodan, the Lord of Sin
 * The Cardinal of Sins and regarded as the Burning Hells' greatest demonic general, Azmodan is a clever manipulator who trades in vice and corruption. Passionate and plotting, he is by far the most charismatic and seductive of the Seven Evils. He loves vice in all its forms, but the truest gratification he derives was that from the failure of others. He is a master of temptation, of causing those who held steadfastly to principles and beliefs to ultimately betray them. He existed only to shred morality, and to bring all within his sphere of pleasure to the point of breaking, believing that all beings find their truest identity by embracing the far limits of perversion and depravity.

Trivia

 * The Seven Evils are based on the demon lords from the Diablo franchise