Dagon

Diagon is believed to have visited Earth many years ago and given 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
Diagon is similar to Vilgax's true form: a giant green squid. His "natural" form is extremely large; dwarfing even Ultimate Way Big.

History
In The Flame Keepers' Circle, Diagon was first introduced and his appearance was revealed in a carving.

In A Knight to Remember, Diagon took control of Gwen and Winston.

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 episode, 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: In addition, Diagon is virtually immortal, he can't be killed by conventional means. Diagon also possesses great knowledge of magic and commands an army of Lucubras and Esoterica.
 * Super Strength: Diagon is extremely strong, as he was able to lift Ultimate Way Big with his tentacles easily.
 * Super 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 can fly.
 * Mind Control: Diagon can control minds like the Lucubra, but Diagon's mind control is much more powerful.
 * Resurrection: Diagon can 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.
 * Lasers:: 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 change into a squid/serpent form which is smaller than his "natural" form and into a dragon form or he can change his size.
 * Regeneration: Diagon can regenerate any damaged parts of his body.
 * Transforming: Diagon can transform others into Esoterica.
 * Teleportation: Diagon can instantly teleport anywhere he wants.

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

Diagon's mind control can be blocked with metal.

He is also 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 (Later absorbed by Vilgax and then sealed within Ascalon)

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 similarites 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 slightly resembles an octopus.