Over the course of the first five seasons, many stories have been told on The CW's "Arrow." We've gone from the past to the present, from the coasts of Lian Yu to outer space. As prime time television's longest running superhero show yet, it set the trend for what types of stories could be told through the medium. As the show progressed, and as the characters and stories evolved and changed, it seems that some story-beats have fallen through the cracks.

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While some of these lost threads may have been nothing more than glorified Easter eggs in the long run, they were tantalizing enough for the comic book fans to get their hopes up in anticipation of what had been teased or established, like setups that never saw a payoff. Along with bigger storylines and characters that have disappeared or are sorely missed from the show, here is a list of 15 loose threads that we would like to see make a return on "Arrow."

15 THE HUNTRESS

Huntress firing her crossbow on Arrow

As early as the seventh episode of the series, we were introduced to Helena Bertinelli, the woman who would become known as the Huntress. Played by Jessica de Gouw, we were given a different, angrier take on the hero, one who was more after vengeance than justice. But after Helena came to visit Starling City for three more episodes over the course of two seasons, we soon came to realize that we were witnessing her evolution, and maybe her rise to the actual mantle of the Huntress.

Her final appearance was in an episode of the second season titled "Birds of Prey," where she came to face against Sara Lance, who at the time was still wearing the Black Canary mask. As comic book fans know, the Birds of Prey are a team of vigilantes mainly consisting of Canary, Huntress, Oracle and a few others. While we never got to see that team in action, this episode ended up as nothing more than a tease for something we wish we could pick up on.

14 THE AMAZO

Amazo boat on Arrow

Back in the flashback story of the first episode of season two, "City of Heroes," viewers witnessed the arrival of a boat on the Lian Yu shore. This was going to be the next big threat for Oliver Queen. When the camera panned to the back of the boat to reveal its name, longtime comic readers were left cheering and wondering at the possibilities that the name "Amazo" entailed. As many know, that is the same name of a very big Justice League villain, the android Amazo, famously known for being able to replicate all the powers of the Justice League members.

Amazo's creator, Professor Ivo, also featured heavily in the flashbacks of season two as one of the main antagonists to Oliver Queen's merry band of survivors. But all of this ended with a dead professor Ivo and a sunken Amazo ship. With Ivo's experiments and quests for superpowers aboard the ship, we were all left wondering if there was something else aboard the vessel, something lurking in the depths of its wreckage. Something that could resurface and pose an unimaginable threat to all of mankind.

13 WALTER STEELE

Walter Steele from Arrow

Walter Steele, played by Colin Salmon, was a big part of the first two seasons of "Arrow" and one of its main recurring players. But after the untimely death of Moira Queen at the hands of Deathstroke, he all but vanished. While we've heard his name mentioned a few times, we still don't know much about what the character is up to, or how he is coping with the loss of his wife.

When we were introduced to him all the way back in the show's first episode, he was married to Oliver's mother after the passing of his father. But not only that, he was also an important character to Oliver's sister, Thea. With her father and brother gone, Walter was there for her and a great father figure to have at her side. After Thea discovered that Malcolm Merlyn was her real father, and after having trained with him and finally cutting all ties with the assassin, she could certainly use a guiding hand from a man who was a true father to her, a man who wanted nothing but the best for her, without any strings attached.

12 KORD INDUSTRIES

Ted Kord Blue Beetle from Batman Brave And The Bold

Kord Industries is a company that has been mentioned in "Arrow" numerous times, one whose logo can be glimpsed from time to time in the Starling City skyline. All in all, it's been seen or mentioned in nine episodes over the course of five seasons, from the Clock King, one of their former employees who attempted to steal one of their devices in "Time of Death," to Oliver Queen's parents attending a fundraiser held by the company's owner Ted Kord in "The Undertaking."

To comic readers, Ted Kord is known as the hero Blue Beetle. Similarly to the Green Arrow or Batman, this version of the Blue Beetle has no superpowers, instead relying on his intellect and vast array of self-designed weaponry to fight crime. While the Arrow producers did mention that there was an earlier plan to use Ted Kord, it was instead dropped in favor of introducing Ray Palmer – The Atom – in season 3. We still hope an understanding can be made with the powers that be to bring the Blue Beetle to Star City.

11 WILDCAT

Wildcat from Arrow

In the early days of the third season, Laurel Lance had begun training for her future role as the second Black Canary under the tutelage of Ted Grant, a boxer and gym owner. We soon came to learn that Ted also used to be a vigilante who went by the name of Wildcat. While this was all a nod to the comic books and Black Canary's history of learning to fight from Ted Grant, it all came to an abrupt stop in the episode "Uprising" when Ted took a beating at the hands of Danny Brickwell.

While he survived the ordeal, we never saw Ted again and Laurel became a full part of Team Arrow. But in the comic books, Ted was also a very important member of the team known as the Justice Society of America, and for having a son who would later also take the mantle of Wildcat. With the JSA having appeared in the second season of "Legends of Tomorrow," we could see Ted resurface and become a part of that team, or see him try to re-connect with his father in the past through the means of time travel.

10 OLIVER QUEEN'S SON

William Oliver's Son on Arrow

One of the big storylines of season four was Oliver discovering that he had a child he never knew he had fathered, a son by the name of William. After William was kidnapped and rescued by his father, Oliver decided it was best for him and his mother to be far away from him in order to be kept safe. Oliver left his son a recording, one that revealed his identity as the Green Arrow.

While William is kept far away, the conclusion of season five and the flashback storyline could bring him back in a big way if "Arrow" were to introduce a page from the "LOST" playbook: flash-forwards. A new storyline set in a future, five to ten years away, could show us William finding his father, now much older, weary and alone, much like in the "Legends of Tomorrow" episode "Star City 2046." We could then see Oliver train his son to become his new sidekick, all while the scenes in the present would all lead us, through the following seasons, to the moment where the team would fracture and having Oliver left all alone.

9 SOLOMON GRUNDY

Injustice Gods Among Us Solomon Grundy fighting Green Arrow

A foil for the first half of season two, Cyrus Gold was the first test subject to survive Brother Blood's experiments and receive superpowers. As comic readers known, Cyrus Gold is the alter ego of the villain known as Solomon Grundy, a super-powered monster who came back from the dead. While Cyrus Gold was neither a grey brute nor a zombie, he was still an antagonist on the rise.

When John Diggle found the Solomon Grundy poem in Gold's apartment in the episode "Three Ghosts," it left us all wondering if the show would actually introduce Grundy. Partial answers came by episode's end when the Arrow defeated Gold by causing an explosion that doused him in chemicals. Gold's skin turned grey and cracked, and he was left for dead. The stage seemed set for the actual villain known as Solomon Grundy to rise from the grave and return to haunt his killer, but we are still left still waiting for that to happen.

8 SLADE WILSON'S FIRST SON

Grant Wilson on Legends of Tomorrow

In "The Odyssey," the second episode to feature Slade Wilson in the flashback storyline, we were informed that Slade had a son, Joe, back home. But when Slade returned in the present storyline to torment Oliver Queen and his friends, he did so without ever mentioning his son again. Neither did Oliver bring up Joe's name in their following confrontations, something he could have easily done to try and bring Slade back from the brink.

While we never saw Joe, we did see another of Slade's sons, Grant Wilson, in the "Legends of Tomorrow" episode "Star City 2046," who took up his father's mantle as Deathstroke. But in the comics, Joe Wilson goes by another name: Jericho. While Jericho is usually on the side of good, an "Arrow" twist could have seen him brought back as a villain. With his power to take control of other people's bodies through eye contact, he would have been a formidable opponent to see Arrow tackle.

7 ARGUS AND THE SUICIDE SQUAD

Arrow version of the Suicide Squad

Season two featured a side-story for Diggle that told of his relationship with Floyd Lawton, a.k.a. Deadshot. This all led to the introduction of Amanda Waller, A.R.G.U.S. and their very own Task Force X, the Suicide Squad. With team members that went from the Bronze Tiger to the possibility of King Shark and even a Harley Quinn tease, it seems that all further plans for the Task Force were squandered when the "Suicide Squad" big screen movie arrived in theaters.

With Waller and Lawton now dead and A.R.G.U.S. controlled by Diggle's wife Lyla, it makes us wonder whatever became of the squad members that were locked up. We know Harley Quinn, King Shark, and whoever else were behind the metal doors are out there somewhere. While a return to the small screen is unlikely for Task Force X, we would sure like to see them being brought back into the fold to answer some lingering questions and wrap up a story that ended too soon.

6 METAMORPHO

Metamorpho from DC Comics

A very obscure Easter egg was slipped in season two in the form of a van that read “Metamorpho Chemical.” While nothing ever came of it, we did hear John Diggle mention that "Metaporpho" was a company in Star City that had been affected by "The Undertaking." While that might not mean anything to casual viewers, the name Metamorpho means a lot to comic readers. It's the alter ego of Rex Mason, the superhero who has the power to transform his body into many elements.

With the chemical company being affected by the earthquake that plagued Star City at the end of the first season, it seemed all but assured that Rex would appear alongside the Arrow at some point. However, that moment still hasn't come to pass. With "The Flash" now well into its third season, super-powers are more than the norm in the "Arrow" universe and it seems like a prime time for the Element Man to arrive and join the ranks of our ever-expanding team of heroes.

5 CONSTANTINE IN HELL

John Constantine hands on fire

NBC's "Constantine" was a series gone too soon. Matt Ryan's energetic, brilliant take on John Constantine was so spot on, so definitive, that it brought him back to the character, from the animated medium to the "Arrow" universe. In the season four episode "Lost Souls," Ryan's Constantine was brought into the fold when it was revealed that his character had a tie to Oliver Queen's past of Lian Yu. After a quick trip to Star City in the present day, Constantine saved the day and left Oliver with a warning.

While we wouldn't see Constantine on the show again, his name was mentioned a few times after that, most notably in the 15th episode of season four, "Taken," where Oliver almost casually mentions that Constantine is actually, literally, in Hell. While that certainly sounds interesting, we are left with a few questions, like how did Oliver come to know this fact, why did Constantine go to Hell, and will he make it out of there? It all begs a return from Matt Ryan's signature character. At the very least, we hope that the upcoming "Constantine" CW Seed animated series addresses this.

4 ROY HARPER

Roy Harper Arsenal

Introduced in the latter half of season one, Colton Haynes became a part of the main cast in season two and three of "Arrow" as Oliver's sidekick Speedy/Arsenal. But after taking the fall for Oliver, Roy had to fake his death and start a new life away from Star City. While he did reappear briefly in the season four episode "Unchained," he passed on his costume to Thea and left the city once again.

With Roy Harper being an important character to the Green Arrow mythos, it would be great to see him return to the place that he called home, and to the team and mentor that made him who he is. In the comic books, Roy has many famous stories under his belt, least of all is one where he loses his arm in a horrific accident, only to see it replaced by a bionic arm. With the presence of the S.T.A.R. Labs team and Ray Palmer's robotic technology, there are many possible ways to adapt this story in the Arrow universe.

3 OMAC/BROTHER EYE

OMAC on Arrow

This is one is for eagle-eyed viewers and long time comic book readers. In season three, Ray Palmer, now at the head of Queen Consolidated, discovered some files of various weapons marked by the initials O.M.A.C. Now, in DC Comics, the OMACs are cyborgs, absolute weapons that target metahumans, and they are all controlled by an entity, a sentient satellite by the name of Brother Eye. If that name sounds familiar, it's because we heard it mentioned on "Arrow" before.

In the season three episode "The Secret Origin of Felicity Smoak," Felicity's old boyfriend came back to terrorize Star City with his cyber-terrorist group called Brother Eye. While there were no mentions of a satellite anywhere, we did catch a glimpse of a screen and an eye keeping watch and threatening the citizens of the city. With Felicity's old boyfriend now dead, it could be possible to see his followers pick up where he left off, hack into the old Queen Consolidated files, learn about OMAC, take control of a satellite of their own, and launch an attack on the world.

2 NYSSA AL GHUL AND THE LEAGUE OF ASSASSINS

Katrina Law as Nyssa al Ghul on Arrow

When last we saw Nyssa Al Ghul, she was the new Ra's Al Ghul and, with the intent of proving herself different from her late father, decided to disband to League of Assassins. But whatever happened to the League and its members? While we never knew their exact numbers, there appeared to be quite a few members in that league, all highly trained assassins who do not necessarily believe in what Nyssa is trying to accomplish.

The ex-assassins could very well decide not to recognize the authority of the new Ra's Al Ghul and choose a new head to govern them. While we saw the League of Assassins a great deal in "Arrow's" first four seasons, there is actually surprisingly little we know about them and what they do for the world, whether for good or for bad. For an organization almost as old as time, their disappearance surely must have left a vacuum, one that some would be more than happy to try and fill, or take advantage of.

1 CAPTAIN BOOMERANG AND SLADE WILSON

Slade Wilson behind bars on Arrow

After his big confrontation with the Arrow, Slade Wilson was left imprisoned in an A.R.G.U.S. prison set up on Lian Yu. While he did return shortly in the third season chapter "The Return," the episode more or less left him in the same condition he started in: back in his cage. But he's not the only super-villain locked up in that prison. There is also a man there, who prefers boomerangs as his weapon of choice, one who was thwarted by the Flash and his friends: Digger Harkness, Captain Boomerang.

As it turns out, in the "Arrow" universe, both Slade and Digger were former ASIS agents, the Australian Secret Intelligence Service. While we have never seen them together on screen, it seems only natural that these two highly trained agents would find a way to break out of their prison and a way off the island. They could then team-up to take on the likes of the Flash and the Arrow, the two heroes responsible for their defeat and imprisonment.

What storylines would you like to see make a return? Be sure to tell us in the comments!