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 according to the legend. Vilgax was mistaken for and later pretended to be Diagon in The Flame Keepers' Circle.

Diagon is in fact an extra-dimensional monster who tried to invade this dimension with help from many Lucubra during Earth's Medieval era. He was banished back to his dimension when Sir George defeated him by cutting out his heart with the Ascalon, a powerful weapon given to him by Azmuth about a millenia ago.

Appearance
Diagon is shown to look similar to Vilgax's true form; a giant green squid as Ben finds Vilgax in the secret room inside head-quarters of the Flame Keeper's Circle to whom the members of the cult worship as the knowledge bringer. But later in A Knight to Remember, Diagon took control of Gwen and uses her to communicate with Ben that Vilgax will attempt to steal the source of his strength, his heart. After that, Driscoll tells Ben that when the First Knight fought Diagon, he reveals that Diagon's true form is somewhat like a Dragon. Diagon scares Gwen as seen in A Knight to Remember and horrifed Ben, Gwen and Kevin into demanding Azmuth to get them away in Solitary Alignment. Azmuth and Sir George do not seem to be scared of Diagon. They have probably gotten used to the sight of him.

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 her attitude saying that his daughter became a worse tyrant than Adwaita ever was. Spellbinder says that he can't stay in Ledgerdomain knowing that his life was bought by the cost of so many others and decides to leave again. Charmcaster says no, but Spellbinder 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 calls for his herald Vilgax to defeat Sir George, but he is nowhere to be found, thus Diagon sends his Esoterca 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 had gotten all of Diagon's power. At the end of the episode, Ben used Ascalon to defeat Vilgax and in consequence Diagon was sealed within Ascalon.

Powers and Abilities
Diagon has the power of mind control like the Lucubras, but is much more powerful.

Diagon's heart is said to have enough power to rule the entire universe.

Diagon is extremely strong, as he was able to lift Ultimate Way Big with his t entacles easily.

Diagon is shown to have powerful fire breath.

Diagon can revive the dead.

Diagon can fire powerful laser beams from his eyes.

Diagon can control the weather (as seen in The Ultimate Enemy: Part 2), he used acid rain to defeat Ultimate Way Big and he used lightning to kill Sir George.

Diagon can change his size as shown in The Ultimate Enemy: Part 2.

Diagon also possesses great knowledge of Mana and Magic.

Diagon can give a portion of his power to other beings as shown in The Ultimate Enemy: Part 1 where he gave Vilgax more power in order to break the Seal.

Known Mind Controlled Victims

 * Gwen Tennyson
 * Winston

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 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 controling powers and both look like a 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.