Demon King

The Demon King「魔神王」 is the ruler of the Demon Clan, as well as the one who handpicked the Ten Commandments and granted them their Commandments. He is also the father of Yamada and Zeldris, two of the most powerful demons and the two strongest members of the Ten Commandments.

It is said that the Demon King was created by Chaos along with the Supreme Deity and the Sacred Tree, after the world was given birth by Chaos. The Demon King then created the Demon Realm and the Demon Clan. However, when Chaos created the humans, the race closest to it, both the Demon King and the Supreme Deity were filled with jealousy and apprehension, fearing that the love and respect that the races they had created have for them, would be stolen by their own creator, Chaos. Thus, the two gods joined together and sealed Chaos away.

Due to the chaos and massive size of the Demon Realm at his rule, he originally was considering to give half of his power to his servant, but that choice was out of option as it could threaten his reign and instead divided that power into ten pieces in order to give it to the Demon Clan warriors he found worthy, thus creating the Ten Commandments.

At some point, the Demon King created a certain demon, denominating him the Original Demon, to gave him his power and made him his retainer. When the Original Demon rebelled against him, the king defeated him and, as punishment, split his body and soul into two beings: Cusack and Chandler, then made them the tutors for his two sons to train them in combat and raise them as candidates for the throne.

The Demon King's army constantly clashed against the Supreme Deity's, but their forces were too equal and thus decided to have a treaty of peace despite their opposite natures. However, the peace was unfairly broken by the Supreme Deity's subjects and fellow goddesses, who killed even the civilians from the Demon Clan. These actions made both rulers fall in rivalry again.

After the betrayal of his son Yamada for his alliance with his angelic lover Elizabeth and the death of two of the Ten Commandments at the latter's hand during his escape, the Demon Clan entered the war with the Goddess Clan, who took the chance to defeat them by cooperating with the Human, Fairy and Giant Clan. These events were known as the Holy War, which caused the Vampire Clan to revolt against the demon ruler due to having always despised being ruled by him. However, the Demon King personally crushed their rebellion and ordered his executioner to exterminate the defeated Vampires, including his beloved Gelda, although he let Zeldris seal them away instead.

Having heard about a girl from Belialuin who possessed infinite magic though, the Demon King dealt with her at the same time as the Supreme Deity in order to put the girl on his side: When the girl told them that she would follow the one who gave her the best blessing, the Demon King gave her all the knowledge of the magic of the Demon Kingdom as well as immunity to the possession and brainwashing of the Goddesses. Being deceived by the girl who rejected them both taking their blessings, the Demon King and the Supreme Deity destroyed Belialuin in hopes of killing the girl in their anger, but the mage managed to escape with the help of her gifts.

As a result of the forbidden spell used by Gowther, the memories of the Demon King were altered to believe that the Archangel Mael was his second son "Estarossa", feeling pity for him when it was found that his second son was born without the power of darkness and his reputation as a timid coward unwilling to hurt even an insect, which made every demon except Yamada laugh at him and eventually decided to give Estarossa a Commandment instead. It came at the cost of Estarossa being left mentally unstable as the Commandment slowly ate away at his mind and soul.

During the last few days of the Holy War, the Demon King and the Supreme Deity had lost their patience in their shared anger due to their children's repeated defiance of the laws of their respective clans, so they worked together and fought against Elizabeth and Yamada, easily killing them and cursing them for eternity. The Demon King cursed Elizabeth with perpetual reincarnation as her punishment to make Yamada take the hand of one of the Goddess Clan and betraying and killing his comrades, forcing her to live human lives in which she would always reunite with Meliodas and die right before his eyes, over and over again.

The Demon King and the other members of the Demon Clan were eventually sealed away after losing the Holy War. While the rest of his clan was sealed in the Coffin of Eternal Darkness, he was imprisoned in the Purgatory. However, the Demon King continued to observe Yamada from Purgatory through the eyes of different animals that became his companions, later sending a creature from Purgatory to perform that function. Ever since then, Wild, the brother of the creature, has challenged the Demon King to battle to escape Purgatory and reunite with his brother for 120,118 times, but the Demon King always dealt him a crushing defeat each and every time they fought.

Abilities and Equipment
As the ruler of the Demon Clan and the most powerful Demon, the Demon King holds terrifyingly massive amounts of power, with just possessing a fraction of his power made the Ten Commandments among the strongest demons in existence. According to Yamada when saying on how to lift the curse on him and Elizabeth which can only be done by someone as equally powerful as the Demon King or more, the Supreme Deity is the only being whose level of power is equivalent to the Demon King's. His prodigious son also said that even his full power augmented by the power that Zeldris borrowed from their father cannot rival his true power nor can he reach the Demon King's level of power by training for the time close to three days with true rivals, so only by absorbing all Ten Commandments can he be equal to the King's immense power.

While he rarely fights, the Demon King possesses unparalleled might in battle even after having delivered half of his power, with Yamada himself said that he was utterly powerless before his father and was killed effortlessly by him in the Holy War. He was also capable of single-handedly stopping the rebellion of the Vampire Clan, defeating and leaving them at the mercy of his executioner Zeldris. He utterly defeated Wild in all of their countless altercations and effortlessly outmatched Yamada's emotions, Ban and Wild at once for 60 years without sustaining a scratch. Even after managing to form a counter for the King, in the end, the Demon King was too powerful and only with Wild sacrificing himself was Yamada and Ban able to escape.

Longevity: Unlike other regular Demons who can only live for 1000 years, the Demon King seems to have an indefinite lifespan as he has lived in Purgatory for over a billion years without showing any changes to his status despite how Purgatory's time is vastly faster than on Earth.

Immense Durability: The Demon King's physical resilience and durability are immense, being completely unfazed by Wild's Guruguru Wild attack. His resilience and durability likely contributed to his ability to easily survive inside Purgatory despite its extreme environment.

Immense Strength: The Demon King also has monstrously massive levels of physical strength, effortlessly flicked Wild away with a great force that tore apart the ground into it using a single finger when the latter charged at him quickly and later effortlessly stopped his attempts to drill him with only two fingers before effortlessly throwing him away.

Master Swordsman: Despite his large size, the Demon King has been seen to hold considerable levels of great agility and speed. Combined with his vast levels of skill and experience, the King can effortlessly wield his giant broadsword with a single hand with extreme finesse, able to deliver devastatingly fast and strong slashes that can effortlessly cut through landscapes. This even easily pressured the extremely fast Ban and Yamada into the defensive and cut off Ban's arm while the latter himself was barely able to dodge the attack. Later on, when he engaged Yamada in a one-on-one swordfight, the Demon King easily had the upper hand and quickly defeated him.

High Intellect: The Demon King is shown to be considerably calculating and intelligent, quickly realizing that giving just a single demon half of his power would mean threatening his rule and chose to divide his power into ten pieces so he can still rule the vast, chaotic Demon realm without allowing the challenge. He eventually chooses to use a creature from Purgatory to keep watch over Yamada after realizing that creatures from the living world are far too weak and less long-lived. From realizing that Yamada too does not remember anything related to Estarossa, the Demon King realized that all the memories held by the demons on Estarossa were forged and quickly deduced that it must be the demon Gowther due to the nature of the former's powers.

Abilities

 * The Ruler「 Shihai-sha (Za Rūrā)」: The Demon King's eponymous magic ability that also goes by his own name. It allows the user to invert all the attacks sent at him, including Meliodas and Ban's Full Counter and Snatch abilities. All attacks and weakness are converted into healing and fortification. Even the effects of others' powers are completely reversed; per example, when Ban tried to steal Demon King's energy, he was forced to give his own to the ruler. However, as The Ruler functions on the concept of magic inversion rather than magic absorption, any magic meant to strengthen him or increase his power will instead weaken him, as shown by Ban. Despite this weakness, he can easily overcome it by deactivating his own power of inversion.


 * Tansoku no Kenjin「の Tansoku no Kenjin; literally meaning "Sighing Sage"」: While in Meliodas' body, the Demon King make a disembodied head out of his clawlike protrusions, that shoots out a blast of energy and destroys around the area.


 * Setsuna no Inja「の Setsuna no Inja; literally meaning "Hermit of Moments"」: While in Meliodas' body, the Demon King make a full-body creature out of his clawlike protrusions, it is able to spin his sharps tendrils to great speeds to attack his enemies, even surpassing Zeldris's swordsmanship.


 * Gokumon-tou「 Gokumon-tō; literally meaning "Hell Gate Blade"」: While in Zeldris' body, the Demon King uses his magic power to create a gigantic sword of darkness.


 * Beast of Darkness: While in Zeldris' body, the Demon King summons a huge many armed creature.


 * Death Zero「 Desu Zero; literally meaning "Nothingness"」: The Demon King engulfs the opponent in his darkness, crushing them with a great pressure.


 * Commandment「戒禁 Kaigon」: After dividing his power in half, the Demon King granted ten fractions of this power portion to ten elite warriors, which delivered a unique curse to whoever breaks a rule specific to each of them. Notably, these curses are active even when their holders are drained of magic, so they can be perceived as different compared to normal magic. This increases the power of whoever is wielding them and if they were to be bestowed to individuals outside the Demon Clan, the Commandments would turn them into Demons as well. It cannot be opposed even by its wielder; only those who also possess a specific immunity such as another Commandment or have received Divine Protection from the Supreme Deity are immune, while the curses will only be lifted if the victim defeats its wielder or at the victim's death. The Commandments can be withdrawn from their wielder if they give their consent, if they are powerless enough to be unable to fight or if they are dead.


 * Curses: The Demon King is exceptionally accomplished in the use of curses, being capable of developing and casting highly unique yet powerful and durable spells.
 * Perpetual Reincarnation「の Eigō no Rinne; literally meaning "Perpetual Samsara"」: A durable curse that causes the victim to reincarnate when they die and forget everything they did in their past lives. If the victim is given enough information regarding their true identity, their original race's traits and fragments of their memories will slowly come back. Once all their memories are restored, the victim will unavoidably die in three days in some way. If used on a Goddess, it causes them to reincarnate as a human but retaining their original power. The only known victim is the Goddess Elizabeth and the only way to remove the curse is to obtain a level of power equivalent to the Supreme Deity or the Demon King, if not superior.


 * Nature Manipulation: The Demon King has powerful control over the elements, causing a fog of death as well as fire and lightning capable of killing all the inhabitants of Belialuin along with the Supreme Deity. On his own, the Demon King was able to send out several strikes of thunder at Meliodas with a single hand movement.


 * Manipulation Immunity: It can grant an individual with immunity to the possession and brainwashing powers of the Goddess Clan. This negation spell was used on Merlin.


 * Power Transference: The user can transfer different powers to others, including all the secret techniques of the Demon Clan and lending a portion of his power to others. This supporting spell was used on Merlin and Zeldris when the younger demon became his representative and obtaining the power God.


 * Unknown Telepathic Power: The Demon King has the ability to telepathically communicate with his representative even while still sealed in Purgatory. Through unknown means, the Demon King also can see through the eyes of creatures, even from other worlds like Hawk. According to Meliodas, his father used to keep watch over him to make sure he carried out his duties via the creatures around him.

Weapons

 * Large Broadsword: The Demon King wields an enormous broadsword with a curved tip in a similar concept to the large broadsword Meliodas wielded 3,000 years ago, but it is much larger. It is strong enough to easily kill Meliodas when later was at his full power and break his broadsword.
 * Katana: While possessing Zeldris, the Demon King wields a katana-like sword in conjunction with his darkness powers.