Marvel Studios has a very strong track record of successful movies on both the critical and financial fronts, to the point that some would say they can do no wrong. They have earned the trust of the audience and the goodwill of longtime comic book fans. Their universe is carefully constructed, and their long-term stories planned in advance. With so many people involved over a long period of time, no one can fault such an unprecedented shared cinematic universe from having a few bumps in the road, or some ideas left behind.

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Cameos and Easter eggs are often used to give fans even more enjoyment out of these movies, something to be on the lookout for, or something that can leave you excited about things to come. However, some of the Marvel Cinematic Universe cameos have proven to be introduced or set-up without any sort of resolution or payoff. Today, CBR takes a look at 15 MCU cameos that turned out to be wasted or mishandled.

15 THE TEN RINGS

Ten Rings Logo Iron Man

Back in the early days of the MCU, there weren't many big villains around. In the first "Iron Man" movie, Tony Stark only had to deal with Obadiah Stane as his main antagonist. But there was another villain hiding in plain sight in the form of the Mandarin. As comic book readers know, the Mandarin is known for having 10 powerful rings on his fingers that he uses as magical weapons. In the movie, however, the Ten Rings were the terrorist organization who kidnapped Tony Stark.

If that wasn't enough of a tease, we got a second, albeit smaller hint of them in "Iron Man 2," where, thanks to the credits, we were informed that the Ten Rings supplied Ivan Vanko with the means to reach Tony Stark at the Grand Monaco race. The stage seemed set for the organization and the Mandarin to make their grand entrance in "Iron Man 3," where we saw the Ten Rings logo in the latter's propaganda videos. But then all of that was undone when it was revealed that the Mandarin was a creation of Aldrich Killian in a bit of a retcon that left us scratching our heads and wondering why there was no actual pay off to the Ten Rings organization.

14 THE HUMAN TORCH

The Human Torch in a tube in Captain America: The First Avenger.

When Steve Rogers, Bucky Barnes and their two dates went to the Stark Expo in New York in "Captain America: The First Avenger," we were given a quick glimpse, an Easter egg really, of another hero in the Marvel Universe: the android known as the Human Torch. Not to be confused with the Fantastic Four's Johnny Storm, this Human Torch fought alongside Captain America in World War II, and together they were a part of a team called the Invaders.

Just like the Howling Commandos, the Invaders were responsible for many victories against the Nazis, and were crucial in winning the war. However, with time being so short in the movie, we only got to see one of Captain America's super-teams in action during the war. With the appearance of the original Human Torch, however, the door is still open for flashback sequences in a new movie, sequences that could show us more battles that Cap and his Invaders fought during the war.

13 BARON STRUCKER

Baron Strucker Avengers

In the mid-credits scene of "Captain America: The Winter Soldier," we saw our first glimpse of Baron Strucker, a member of Hydra, longtime enemy of S.H.I.E.L.D. and the Avengers. The scene showed us a large operation that Strucker was heading, one that led to the creation of the Scarlet Witch and Quicksilver. This left us all excited for "Avengers: Age of Ultron," a movie that started with a sequence of our heroes assaulting Strucker's castle.

It wasn't much of a surprise to see that Strucker was caught by the likes of Captain America, and we thought we would see Strucker return some time later in the film, or another one entirely. The real surprise came a bit later, when we came to learn that this big Marvel villain had been killed off-camera by Ultron in his prison cell. Fans were left disappointed by Strucker's much-earlier-than-anticipated demise and lamenting what could have been.

12 DOC SAMSON

Doc Samson in The Incredible Hulk

Viewers may have forgotten this since it was nearly 10 years ago, but "Modern Family" veteran Ty Burrell co-starred in "The Incredible Hulk" as Betty's post-Banner boyfriend and psychiatrist Doctor Leonard Samson. He didn't play a big part in the movie and never even addressed Bruce Banner directly, but he was an established character and had enough of a strong personality to stand up to Betty's father, General Thaddeus Ross.

In the comic books, Doc Samson is also affected by gamma radiation and develops super-human strength and green hair. Although not nearly as powerful as The Hulk, Doc Samson is still a part of his supporting cast and a dependable ally (well, before he became evil). It sure would be interesting to see Ty Burrell return to the role and become a super-hero, but the fact that the Hulk is only appearing in team-up movies and that there are no "Hulk" sequels in development doesn't seem likely we will ever see Doc Samson return to the screen.

11 ADAM WARLOCK

Adam Warlock Cocoon Guardians

The fan-favorite cosmic character made his cinematic debut in the mid-credits scene of "Thor: The Dark World," when Volstagg and the Lady Sif entered the Collector's domain to deliver him the Aether. It was there that we saw, in a glass case, Adam Warlock's cocoon, as part of the Collector's dear collection. Casual moviegoers may not have noticed this, but the inclusion of this cocoon, or egg, was very promising for the future of the cosmic side of the MCU.

Marvel readers are familiar with Adam Warlock's ability to enter a cocoon whenever he needs to regenerate or heal. When the Power Stone destroyed part of the Collector's keep in "Guardians of the Galaxy," it was unclear what became of the cocoon, but one could easily think that the egg was cracked open and that the Soul Stone-wileding Adam Warlock could be set free. His awakening would have led to him roaming the spaceways, and arriving to lend a powerful helping hand in the fight against Thanos. Fingers crossed this still may happen.

10 THE LEADER

Samuel Stearns begins to become The Leader in The Incredible Hulk

In "The Incredible Hulk," professor Samuel Sterns arrived late in the game to help Bruce Banner find a cure for his gamma poisoning condition. At the start of the film, we knew that Banner was in contact with someone who was helping him, someone to whom he was sending vials of his blood, but we didn't know who. When it was revealed that Sterns was the mind behind the Mr. Blue identity, fans rejoiced at the idea and the potential that entailed.

As The Leader, Samuel Sterns is a very big Hulk and Avengers villain, one with green skin and an enlarged head. We saw a glimpse of the villain in the movie when it was revealed that he had been conducting many experiments with Banner's blood, and later on when the Abomination trashed his lab, leading to a few drops of Banner's blood to leak onto an open wound, which caused his head to mutate. Sterns was left smiling, and we were left wondering when we would ever see the Leader resurface.

9 THE COLLECTOR

Infinity-Gauntlet-GuardiansoftheGalaxy-Collector-5

When Benicio Del Toro was cast as The Collector, we were told that he would feature prominently in the Marvel Studios movies moving forward. But after a mid-credits sequence in "Thor: The Dark World" and a very small role in "Guardians of the Galaxy," fans have yet to see The Collector play an important role in the MCU. His first appearance teased at his involvement with Thanos and the Infinity Stones, but we haven't see anything after that which could point to him having a bigger role in future movies.

As an Elder of the Universe, the Collector is billions of years old. Immortal and powerful, he plays a big part in the cosmic events that shape the Marvel Universe. However, in the MCU, there is little actually known about the character, and even less to convince us that he is an all-powerful alien as old as time. Here's hoping that we will see much more of the Collector in either "Avengers: Infinity War" or "Thor: Ragnarok," where his brother the Grand Master will make his cinematic debut.

8 ELLEN BRANDT

Ellen Brandt in Iron Man 3

Ellen Brandt had a small role in "Iron Man 3" as one of Aldrich Killian's Extremis soldiers. As a war veteran, Ellen joined AIM to be injected with the virus to become a thorn in Tony Stark's side. But there was one thing that Marvel readers noticed about the character: a scar, on her face, just like in the comic books. This scar she got after accidentally creating the living swamp-like monster Man-Thing, the man who used to be her husband, Ted Sallis.

As an agent of AIM, Ellen attempted to acquire her husband's research only to lead to an accident that turned him into this creature that left her scarred. We don't know if Ellen was married in the movies, and we are not even sure she survived her confrontation with Tony Stark. But one thing we do know is that her existence could seemingly confirm the existence of Ted Sallis and the creature known as Man-Thing.

7 JAMES MONTGOMERY FALSWORTH

James Falsworth in Captain America The First Avenger

Recruited by Steve Rogers after his heroic mission to save hundreds of prisoners from Hydra's clutches, James Montgomery Falsworth became a member of the Howling Commandos in "Captain America: The First Avenger." He did not have the biggest role or much in the way of development, but he made up for it with a joyous personality. But in the comic books, Falsworth went by another identity. As a British Lord and government agent, James also goes by the identity of Union Jack, essentially the British version of Captain America.

Draped in his country's flag and colors, Falsworth fought in both the First World War and the Second. He also joined Captain America's team of Invaders, a team that also included the Human Torch, as previously mentioned in this list. Sadly, we may never see Falsworth don his mask and costume, though the use of flashbacks could always remedy that. If not for his time in the war, it would be easy to explore how Falsworth was inspired by his deceased friend Steve Rogers to keep on fighting in his country's name.

6 COSMO

Cosmo in Guardians of the Galaxy

The Soviet dog Cosmo appeared very briefly in "Guardians of the Galaxy" as a part of the Collector's extensive display on Knowhere, the giant space port inside a severed celestial head. He bared his teeth and growled at Rocket, who responded in kind. As a telepath, it would have been great to hear Cosmo actually talk and interact with the rest of the Guardians, considering he becomes an official part of the team in the comic books.

Later in the movie, Cosmo was freed thanks to the destruction of the exhibit. After the Power Stone explosion, we quickly saw him roam freely on Knowhere, the place he assumes total control and protection of in the books. We never saw what became of Knowhere after the Guardians left it, but fans could easily picture Cosmo rising up to the occasion after Ronan's attack and establishing a new, well-ordered rule over the space port, a port that the Guardians could very well come to call home.

5 KING T'CHAKA

TChaka in Civil War

As the King of Wakanda, T'Chaka arrived at the United Nations in "Captain America: Civil War" after a disaster that left some of his citizens dead. But he was only a pawn in Zemo's game, and he died in a tragic explosion. His appearance was very brief, and his departure quite sudden. Granted, this development occurred to send his son T'Challa, the Black Panther, on a quest for vengeance, hunting for the Winter Soldier, the man he thought responsible for the explosion.

But T'Challa's rise came at the cost of his father's character. King T'Chaka had a long history in the comics books, one that saw him protect his country long before his son ever did. As the Black Panther, T'Chaka fought for Wakanda and the precious metal that hails from it, Vibranium. In the books, he was murdered by Ulysses Klaw, who harbored a family feud with the good King, a character who has appeared in "Avengers: Age of Ultron," and this created a long rivalry between T'Challa and Klaw.

4 THE WASP

The Wasp in Ant-Man Flashback

The "Ant-Man" movie showed us that after Captain America, Iron Man was not the first super-hero in the world. We came to know that Hank Pym worked for S.H.I.E.L.D. as the Ant-Man back in the '80s, and helped save the world from nuclear catastrophe. But, on top of that, he wasn't alone. Through all of that, his wife Janet was also by his side as the Wasp, and she proved to be a true selfless hero when she sacrificed herself to save everyone.

We later came to learn that it's quite possible that Janet did not in fact die that day and that she could actually have been a prisoner of the Quantum Realm. With Hope now poised to take her mother's place as the new Wasp, it is unlikely that we will ever see the original Wasp after an extremely brief cameo appearance. This isn't to say that we might never see Janet again, though. With the "Ant-Man and the Wasp" sequel coming, we really hope Janet will make it out of that realm.

3 A.I.M.

Iron Man 3 AIM

In "Iron Man 3," Advanced Idea Mechanics were finally introduced. A pretty big villainous organization that can match Hydra in size, reach, power and influence, AIM was more or less reduced to a few faces including Aldrich Killian, Eric Savin and Ellen Brandt, and other nameless Extremis soldiers in the movie. The organization was seemingly defeated with the death of Killian, and unheard of again. But the true AIM could never be taken down so easily.

The prospect of AIM as a new villainous organization in the MCU was promising, with Hydra having already played a very large role in almost three movies. AIM should have been allowed to stay and grow in the vacuum left by Hydra. This isn't to say that we would love to see AIM evolve into their usual depiction of yellow beekeeper-like outfits, but a nod in the right direction would go a long way to give the villainous organization the proper representation it deserves.

2 CROSSBONES

civil war crossbones

Brock Rumlow was introduced early on in "Captain America: The Winter Soldier" as a part of Steve Rogers S.T.R.I.K.E. Team, one who seemed to look at Cap with respect. But when it was revealed that Hydra had infiltrated S.H.I.E.L.D. to the highest levels, Rumlow showed his true colors and proved to be the classic villain comic book fans know as Crossbones. The movie made a point to show us that he had survived the Triskelion destruction, and he was primed to return in a sequel.

Return he did, in "Captain America: Civil War" for an opening mission that left us breathless. In his trademark mask and costume, Crossbones led the New Avengers on a chase for possession of a dangerous virus. He fought Captain America hand-to-hand and held his own for a while, but was ultimately defeated. Fans were then left perplexed and disappointed when Rumlow killed himself in an attempt to take Steve Rogers along with him; all of this took place in the opening moments of the movie.

1 THE NOVA CORPS

guardians of the galaxy nova

The Nova Coprs is an intergalactic police force tasked with keeping the peace in the cosmic side of the Marvel Universe. As seen in "Guardians of the Galaxy," they are based on the planet Xandar and are led by Nova Prime. However, this is where the similarities between the movie and the comics end. In the film, Corps members are depicted as regular officers with no real powers. Their most impressive display was in connecting their spaceships to create a field to try and stop Ronan from attacking their planet, something that failed spectacularly.

But in the comics books, the Nova Corps members have access to the Nova Force, great power that allows them to harness energy, fly through space, regenerate and even develop super-human strength. Their levels of power depend on their rank, with Nova Prime being the most powerful of them. But nowhere in "Guardians of the Galaxy" were the Nova Corps shown to possess such, if any, powers. They are supposed to be a formidable group, and we can only hope to see them turn into the true police force they are supposed to be further down the line.

Any other wasted cameos we might have missed? Be sure to let us know in the comments!