Dark Ones (The Evil Dead)

The Dark Ones, known by many alias, are dark entities who serve as greater scope villain of Evil Dead series. They initially made appearance in comic book adaptations of the franchise before finally scheduled to make canonical appearance in TV Series.

Little is known of the appearance of the Dark Ones except for the possible illustrations found in the pages of the Necronomicon Ex-Mortis. The illustrations depict beings of vast size and power, though it is likely that the true image of the Dark Ones is unfathomable to humans, and actually seeing one would drive them mad.

In Ash vs Evil Dead, Dark Ones' characteristic further elaborated on. They are stated to “neither demon nor fully human” who appeared to be humanoid entities dressed in dark hooded cloaks that completely conceal their appearance. One of them, "Ruby Knowby", creator of the very Necronomicon which plague Ash, can also shapeshift into a human form as alternate method.

Army of Darkness vs. Re-Animator
The Dark Ones' debuts. While locked up in Arkham Asylum, Ash Williams encounters The Dark Ones when they are summoned by Herbert West and Dr. Whateley who is a mentor of West. As the eldritch deities begin to emerge from an open portal, Ash manages to destroy The Necronomicon that had opened the portal and had it closed before any of the Dark Ones could escape, causing Arkham Asylum to collapse on itself.

Evil Dead 2: Cradle of the Damned
Dark Ones are mentioned. When Annie Knowby and Simulacrum Ash (a copy of Ash created from Ash's severed hand mixed with Annie's spellcasting using her own blood. But unlike the Canonical counterpart from Ash vs. Evil Dead which was also made from Ash's severed hand minus Annie's blood, this version of Ash copy is a heroic man) are sucked into the Mirror Dimension (aka Deadlands), they encounter a man named Regardie, who has been trapped the said dimension since the turn of the 20th century. When Regardie first arrived, his soul was taken by a Dark One, trapping him in the dimension for all eternity.

Evil Dead 2: Dark Ones Rising
Only one of the Dark Ones, Cthulhu, makes its appearance as the comic's main antagonist. It appears through a sinkhole that connects between human world and mirror dimension, sucking souls of all around the area. Annie Knowby and Simulacrum Ash unleashes souls of some of the most powerful voodoo sorcerers of the last century to aid them in the battle against Cthulhu.

The souls came together to form Damballa, the creator of life. Cthulhu was ultimately defeated by Damballa. Thinking that the battle is won, Annie and Simulacrum Ash looks for a place to feed themselves only for Cthulhu's hand appear out of nowhere and crushes Annie and Ash. It is revealed that they never left Mirror Dimension / Deadlands and are still trapped within the eldritch dimension. The experience Annie and Simulacrum Ash went through was a test to see if souls on Earth was worth taking.

Past
Eons ago, Dark Ones, with their supernatural god-like powers, wreaked incredible havoc upon human realm and humanity found itself at their mercy. There seemed to be no ways of stopping their madness, until one of them named Ruby Knowby, back then known as Mulier Daemonium de Igne (Demonic Woman of Fire in Latin), with the help of her partner in crime Kaya the Necromancer betrayed the rest of Dark Ones and cast them off to an alternate dimension known as Deadlands (Mirror Dimension in comics). Ruby committed the act of treachery for her esoteric agenda but it can be presumed that she wanted to take over the human world for herself.

To the Present
For the next thousands of years, the Dark Ones remained trapped in the place called "Deadlands" until various events of season 3 caused "The Rift", a phenomenon in which magical seal responsible for keeping the Dark Ones imprisoned in the Deadlands, started to become weaker and the portal that would enable Dark Ones to cross over into human world had been established (but not yet in its full power).

It is foretold by the Necronomicon that the Dark Ones will be ultimately unleashed from their dimensional prison, walk upon the human realm once again and the Prophesied One will rise up to stop them. Ruby, tipped off by Kaya from Necronomicon, who after aiding Ruby sealing away Dark Ones, ended up losing her body by the destructive power of Necronomicon and having her soul trapped within the accursed book.

Realizing that the prophecy foretold is in motion and that the Dark Ones, once freed will be coming after her, hatches a plot to anticipate the Dark Ones' coming in her own way: to have the powers of the Prophesied One transferred to her own demonic offspring (a being born from Ruby made in the image of Prophesied One) and to herself. This way, she believes that not even the Dark Ones would be able to touch her. As Ruby advances her devious plot, the seal increasingly weakens and the Rift becomes wider as episodes progress.

However, Ruby's grand scheme is foiled when her demonic Prophesied-One-to-be is killed by the real Prophesied One, leaving Ruby with little option with so little time against impending arrival of her former brethrens.

It is said that upcoming episode "Judgment Day", Dark Ones will be finally unleashed from their dimensional imprisonment and are eager to collect their overdue debt (with interests) from the the pair of women who sealed them in Deadlands thousands of years ago: Ruby Knowby and Kaya.

Other Reference
The Dark Ones are mentioned by Ash as the supposed writers of the Necronomicon Ex-Mortis in the video game Evil Dead: A Fistful of Boomstick.

Trivia

 * Dark Ones are referred to "Old Ones" or "Great Old Ones". But in Cthulhu Mythos, from which these beings are based on, Old Ones and Great Old Ones are two totally separate beings.