Diagon

"You, are a slightly larger speck than the other specks infesting this world. But still, you are beneath my notice."

- Diagon while Ben (as Ultimate Way Big) battles him.

Diagon is a major antagonist in Ben 10: Utlimate Alien, serving as the main villain of season 3, and he is a squid-like alien creature who took a form of a dragon.

Diagon is the founder of a modern day religious cult known as the Flame Keepers' Circle who believed that he have visited Earth many years ago and gave humans advanced technology. He is believed to have sworn to come back to Earth and bring the "Golden Age". He said he will bring alien tech so Earth would have no war, no disease, just peace. Vilgax was mistaken for and later pretended to be Diagon in "The Flame Keepers' Circle".

Diagon is in fact an extra-dimensional demonic entity who is at least 1700 years old and have tried to invade this dimension with help from many Lucubras 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 centuries ago.

Appearance
Diagon is shown to look similar to Vilgax's true form; a giant squid as Ben finds Vilgax in the secret room inside head-quarters of the Flame Keepers 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 scared 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 it.

Though he looks like Vilgax's true form that has the appearance of an octopus, Diagon is in actuality, a powerful demon, not an alien.

History
in "The Flame Keeper's Circle", Diagon was first introduced and his appearance was revealed in a craving at the headquarters.

In "A Knight to Remember", Diagon took control both 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, his voice was heard again when Sir George demand to face him instead he summoned Vilgax his Herald.

In The Ultimate Enemy: Part 1, the Seal was finally broken, allowing Diagon to return to Earth's dimension.

In The Ultimate Enemy: Part 2, Diagon fights against Ultimate Way Big and defeats him with acid rain, later Diagon is absorbed by Vilgax. At the end of the episode, Ben used Ascalon to defeat Vilgax and in consequence killed Diagon, his power transformed into the form of a star because of Azmuth.

Powers and Abilities
Diagon has the power of mind control like the Lucubra, but more powerful. His heart is said to have power enough to rule the entire cosmos.

Diagon is also shown to have powerful fire breath.

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.

Appearances

 * A Knight to Remember (in Gwen's body and flashback)
 * Solitary Alignment (shadow)
 * The Enemy of My Frenemy (voice)
 * The Ultimate Enemy: Part 1
 * The Ultimate Enemy: Part 2

Trivia

 * Diagon is based on the works of H.P. Lovecraft:
 * He is named after the mythological Dagon, a deity in multiple polytheistic religions (Semitic grain and fish god and a major member of the Philistine Pantheon), better known in popular culture for his portrayal in the Cthulhu Mythos, which led to the popular image of Dagon as an incomprehensible, alien deity.
 * Diagon shares some similarites with Cthulhu: both are supernatural aliens, both have mind controling powers and both look like an octopus.
 * Diagon's relationship with the Flame Keeper's Circle cult may be based on the Church of Starry Wisdom that worships the Haunter of the Dark, an avatar of Nyarlathotep.
 * Diagon has been confirmed in the credits of The Enemy of My Frenemy as "The Old One" by Charmcaster which references primarily the Great Old Ones from the stories of H.P. Lovecraft. It may also be a nod to the Old One from the videogame Demon's Souls and the Old Ones from the Justice League animated series.
 * Diagon's dimension is presumably based on the sunken city of R'lyeh.
 * When Diagon was first mentioned, it was said that he looked like a giant squid like Vilgax, but then to relate back to George's character was said that he was a dragon.
 * In A Knight to Remember when Vilgax obtained Diagon's heart, Diagon made Vilgax go to his dimension.
 * Diagon having no heart is similar to Davy Jones (Pirates of the Caribbean) having no heart either. In addition, both hearts are artifacts of immense power.
 * Also of note is the fact that Davy Jones, particularily his head, also slightly resembles a squid.
 * Diagon's dragon form is similar to that of Malchior of the Teen Titans animated series.
 * Though many believe Diagon to be an alien, he is in actuality a powerful demon.