Diagon

Diagon is believed to have visited Earth many years ago and gave humans advanced technology. He is believed to have sworn to come back to Earth to bring the "Golden Age". He claimed he will bring alien technology so that Earth will not have war, nor disease, just peace. Vilgax was mistaken for and pretended to be Diagon in The Flame Keepers' Circle.

Diagon is in fact an extra-dimensional demonic entity who tried to invade this dimension with the help of his Lucubra army during Earth's medieval era. He was banished back to his dimension when Sir George defeated him by cutting out his heart with Ascalon, a powerful weapon given to him by Azmuth nearly two thousand years ago.

Appearance
In the story of St. George and the Dragon, Diagon was pictured as a green dragon. In reality, Diagon is similar to Vilgax's true form: a giant green squid; its "face" is a large mass of tentacles, with what is either a much larger tentacle sticking out of its back or a tail. It has red eyes, and has markings around said eyes. His "natural" form is extremely large; dwarfing even Ultimate Way Big.

Personality
Diagon is a very arrogant being who is shown to be excessively power hungry. Due to the fact that he himself is power, he sees himself as a very godlike and invincible being who deserves to rule all with his mind control. He talks down to all others as if they are merely nuisances or specks (even referring to some as such). Despite this, the Diagon does have a sense of honour to the strong and a sense of caution in dealing with them. He addresses Old George as George the Triumphant due to his past victory against him. He also seems to respect Gwen Tennyson or at least her power. He sent Vilgax to deal with Sir George and Ben due to the danger that George presented.

History
In The Flame Keepers' Circle, Diagon was first introduced as a legendary alien god who is believed to have brought the technology to humans in the past, and which in its turn to bring "The Golden Year" for Earth and his appearance was revealed in a carving.

In A Knight to Remember, Diagon took control of Gwen and explains to them that if Vilgax gets his heart, that he will be able to take control of the entire universe. After Vilgax defeats The Forever Knights and The Esoterica, Diagon takes control of Winston and tells him that in order to be powerful enough to rule the Universe he must break The Seal, however this was a trick.

In Solitary Alignment, his shadow was seen in a flashback.

Diagon's voice was heard in The Enemy of My Frenemy, being called by the name Old One, a being who can bring dead people back to life. Charmcaster gave him six hundred thousand souls (from every living thing in Ledgerdomain except herself) and in return, asked to bring her father back to life. Spellbinder disapproves of this, saying that his daughter became a worse tyrant than Adwaita ever was by doing so. Spellbinder says that though he loves her, he can't stay in Ledgerdomain with her knowing that his life was bought by the cost of so many others and decides to leave again. He returns to the dead and the Diagon makes all souls return to their bodies, saying that "such is the way of magic".

In The Beginning of the End, Diagon's voice was heard again when Sir George demand to face him but instead summoned his herald Vilgax.

In The Ultimate Enemy: Part 1, Diagon was able to turn every human into a Esoterica except for Ben's Team, Julie, and Sir George. Later he took control of Gwen again and he tried to use her to break The Seal. Eventually, he broke The Seal himself, thus allowing him to enter Earth's dimension.

In The Ultimate Enemy: Part 2, After Diagon freed himself, Sir George immediately attacks him, Diagon ordered his herald Vilgax to destroy Sir George, but he is nowhere to be found, thus Diagon sends his Esoterica to defeat George. While Gwen, Kevin and George fight a couple of Esoterica, Ben transforms into Way Big, and Way Big transforms into Ultimate Way Big. Diagon fights Ultimate Way Big and defeats him with acid rain, later he fights Sir George and Chromastone. After he defeats Chromastone and kills Sir George, Vilgax and Psyphon return with the machine. Thinking it's a weapon, Diagon used his laser beams to destroy it, however the machine absorbs powers from other living beings and due to Diagon's essence being only power he was fully absorbed within the machine. Psyphon fired the machine at Vilgax and he received all of Diagon's power.

At the end of the battle, Ben used Ascalon to defeat Vilgax by absorbing Diagon into it.

Powers and Abilities
Diagon is a near-omnipotent extradimensional "demon". His heart alone is said to have the power to reshape the universe itself, and he claims that "his substance is power". His abilities include, but are not limited to: Diagon possesses great knowledge of magic.
 * Enhanced Strength:
 * Diagon is extremely strong, as he was able to lift Ultimate Way Big with his tentacles easily.
 * Enhanced Durability:
 * Diagon is extremely durable, as he was able to take multiple hits from Ascalon and Ultimate Way Big's cosmic rays and disks.
 * Flight:
 * Diagon has the ability to fly.
 * Mind Control:
 * Diagon can control minds like the Lucubra, but Diagon's mind control is much more powerful. It should be noted that he took over an entire planet within seconds. Three known defenses are present:
 * If the victim's head is protected by certain metals, Diagon will be unable mind control the victim.
 * Mana can protect someone from mind control, as Gwen used it to protect herself, Kevin and Ben from mind control; however is should be duely noted that while this defended her on the first wave, Diagon was eventually able to control her. It stands to reason that Mana could protect someone from a mind control wave that was fairly wide spread, but a more concentrated wave could penetrate the mana force field.
 * Ascalon protects the user from Diagon's mind controlling powers.
 * Resurrection:
 * Diagon has the ability to revive the dead.
 * Fire Breath:
 * Diagon is mentioned to have powerful fire breath.
 * Power Bestowal:
 * Diagon can give a portion of his power to other beings.
 * Laser Beams::
 * Diagon can fire powerful laser beams from his eyes.
 * Weather Control:
 * Diagon can summon acid rain (used to defeat Ultimate Way Big) and lightning (used to kill Sir George).
 * Shapeshifting:
 * Diagon can shapeshift into a squid/serpent form (which is smaller than his "natural" form), a dragon form and he can change his size.
 * Regeneration:
 * Diagon can regrow severed tentacles.
 * Transforming:
 * Diagon can transform other beings into Esoterica.
 * Teleportation:
 * Diagon can teleport anywhere he wants.
 * Immortality:
 * Diagon is virtually immortal, he can't be killed by conventional means.

Weaknesses
Diagon's essence is power, which makes him vulnerable to having his power (and thus himself) absorbed by another.

Diagon's mind control can be blocked by protecting the head with certain metals.

Diagon can be hurt by Ascalon.

Diagon is bound to the rules of magic, shown when returning the payment of the souls of Ledgerdomain when a bargain had been refused.

Known Mind Controlled Victims

 * Gwen Tennyson
 * Winston
 * Unnamed Forever Knight (via Lucubra)
 * Unnamed Forever Knight (via Lucubra)
 * Unnamed Police Officer (via Lucubra)

Appearances

 * The Flame Keepers' Circle (carving)
 * A Knight to Remember (voice; flashback)
 * Solitary Alignment (shadow)
 * The Enemy of My Frenemy (voice)
 * The Beginning of the End (voice)
 * The Ultimate Enemy: Part 1 (first appearance in person)
 * The Ultimate Enemy: Part 2

Trivia

 * Diagon is named after the mythological Dagon, a supernatural being who has taken many identities such as the Semitic grain and fish god and a major member of the Philistine Pantheon.
 * Diagon himself appears to be based on the Dagon from H.P. Lovecraft's short stories which subsequently lead to the popular image of Dagon.
 * Diagon shares some similarities with Cthulhu: both are aliens, both have mind controlling powers and both look like an octopus. In The Enemy of My Frenemy, Charmcaster calls him "the Old One." Cthulhu's species were known as "The Great Old Ones."
 * Diagon having no heart is similar to Davy Jones (Pirates of the Caribbean) having no heart either.
 * Also to note of Davy Jones, particularly his head, also resembles an octopus.