SPOILER ALERT! Spoilers ahead for multiple Marvel Comics stories.

Over the course of their storied tenure as the Marvel Universe’s premiere superhero team, the Avengers have been rebuilt, restructured, assembled, disassembled and reassembled again so many times it’s hard to keep track of just how many different incarnations there have been over the years. Just about anybody who’s anybody has been a member and even if they haven’t always boasted the most powerful heroes around, the Avengers have always boasted the best the Marvel Universe has to offer. Well, most of the time…

RELATED: Avengers & X-Men: The 15 Greatest Crossovers

Currently the franchise is undergoing another period of rebuilding in the wake of the second superhero Civil War and all-new, all-different Avengers stand ready to embark on a new era of adventures. With that in mind, we thought it was a great time to remind everyone of all of the great – and not-so-great – Avengers you may have forgotten about over the years.

15 The Forgotten One

First up is the aptly dubbed Forgotten One. Perhaps best remembered for his cold-blooded murder by one of Immortus’ temporal henchmen, the Forgotten One is one of the ancient Eternals and has wandered the Earth for millennia, a proto-legend mistaken for many of history’s greatest heroes, including Samson, Gilgamesh and his good friend and brother-in-arms Hercules. The Forgotten One even performed one of Hercules’ famous labors, cleaning the stalls of the perilous Augean Stables by diverting the flow of two rivers.

Taking the name Gilgamesh, he served with the Avengers during one of the lowest points in the team’s history, sacrificing his life while recovering from severe injuries sustained during a battle with Blastaar. As a member of the Gods of War, Hercules’ ragtag team of earthbound demigods, Gilgamesh has once again re-entered the public eye, lending his bulging biceps to defeat the new gods of the Uprising Storm. In fact, it is by Hercules’ side that he may have performed his most important labor to date: pushing the Lion of Olympus to take his legacy more seriously and reclaim his mantle as the world’s first true superhero.

14 Demolition Man

There was a time when it seemed like just about anybody could join the Avengers. For some, it could be argued, the previous sentence is all the description this entry really requires. Known more for his undeniable body odor, Dennis Dunphy is used to being underestimated. About the only person who ever game him a fair chance was Captain America, who somehow finagled D-Man an honorary Avengers membership.

A product of the Power Broker’s experimental superhuman augmentation process, Demolition Man is a superhuman powerhouse with incredible strength and endurance. D-Man’s effectiveness is largely defined by his own self-confidence, which was severely damaged after Titania brutally beat the holy hell out of him and threw him off a cliff. For a brief time, he toyed with being a villain as part of Wonder Man’s ill-advised Revengers squad, but most recently, he’s back at Cap’s side, freshly washed and outfitted, as ground support and field back up.

13 Lionheart

The role of superhero has never come easy to the woman called Lionheart. A single mother of two and a schoolteacher, Kelsey Leigh was chosen to take up the mantle of Captain Britain, after selflessly throwing herself in the path of danger to save the life of Captain America. Given a choice between the Sword of Might and Amulet of Right, the poorly-informed Kelsey chose the more violent first option and was subsequently cut off from her children.

She served for a time with the Avengers until they were unceremoniously disassembled by Brian Michael Bendis and David Finch. After surviving the Avengers’ latest implosion, Kelsey returned home to Jolly Olde and ran afoul of Excalibur and her former benefactor Brian Braddock. Maddened by her prolonged separation from her children, Lionheart came under the influence of Albion, who used her in his beef with Captain Britain. Kelsey eventually came to her senses and turned on the inter-dimensional despot, aiding Excalibur in his capture.

12 Firebird

Firebird holds the dubious distinction of being passed over for Avengers membership by the opportunistic Hawkeye, who had his eagle-eyes set on the higher profile Ben Grimm. Maybe she shouldn’t have been so needy and told Mockingbird it was her dream to serve with the Avengers. Maybe she should’ve played hard to get, like the Thing did, when he bailed on Hawkeye’s offer at the last minute. Whatever the case, Firebird’s career as a hero has largely unfolded without much fanfare. She’s appeared a few times over the years to aid the Avengers whenever they need someone of her precise skill set but otherwise flies in the shadow of other more visible fire-themed heroes.

Her convoluted back story and well-documented crisis of faith indicate a decided lack of focus when it comes to her character development. She originally started out as a devout Catholic but has since been seen embracing her Native American heritage. In short, nobody seems to know what to do with Firebird, except Firebird herself, who presumably continues to protect the American Southwest with her friends in the Rangers, waiting for the next call up to the Big Show.

11 Triathlon

Although better known nowadays as the 3-D Man, Delroy Garrett originally joined the Avengers as Triathlon. At the time, the disgraced Olympic athlete was acting as the spokesperson of the Triune Understanding, the insidious religious cult that gave him his powers. Using the power of public opinion to smear the Avengers in the press, Triathlon was recruited by the team in an attempt to improve their PR image. Triathlon eventually bailed on the Triune Understanding when it was revealed they had stolen the original 3-D Man’s “triangle power” to fuel Triathlon’s transformation and make contact with a source of immense cosmic energy.

After he thwarted the cult leader’s bid for godhood, Triathlon parted ways with the Avengers, only returning for a brief stint as an instructor for Tony Stark’s 50 State Initiative. He played a pivotal role during Secret Invasion, using the original 3-D Man’s goggles to expose Skrull imposters who had infiltrated the superhero community, and later joined Jimmy Woo’s reformed Agents of Atlas, in an effort to further explore his burgeoning powers. He appeared briefly during AXIS as one of Doctor Doom’s Avengers but has since faded back into obscurity, awaiting his next shot in the spotlight.

10 Stingray

A brilliant oceanographer who first donned his signature underwater battlesuit to capture the Sub-Mariner, Walter Newell eventually became one of Namor’s staunchest allies for years. In the years since his debut, Stingray has become the Marvel Universe’s undersea point man, stepping up whenever the Avengers or the Fantastic Four need an undersea expert who brings something more to the table than just pointy ears and a chip on his shoulder the size of Manhattan. Stingray served with the Avengers in various capacities over the years, perhaps most notably as the caretaker of the now-defunct Hydro-Base.

Most recently, Captain America tapped him on the shoulder to infiltrate Deadpool’s shady Mercs for Money organization, where he was forced to impersonate Wade Wilson in a bid to increase his visibility on the world stage. Although not exactly a dream gig, Stingray performed his duties admirably but quickly hit the bricks with the rest of the Mercs, when Deadpool’s sketchy bookkeeping and incessant abuse became intolerable. In truth, there wasn’t much beyond his duty to Captain America keeping him on the team, but how bad are things on the job, when you can’t even keep Stingray on the payroll? Just sayin’.

9 Living Lightning

Presumably created as an attempt to inject the Avengers with a much-needed dose of diversity, Miguel Santos never achieved his full potential as an Avenger and after a relatively short tenure, left the team to pursue his education. Always a bit of a cardboard cut-out lacking true originality, the Living Lightning probably deserved his status as little more than a footnote in Avengers history. Despite a handful of cameos over the years, Miguel steered well clear of the spotlight – that is, until that time Dan Slott outed him during one of the Great Lakes Avengers unsuccessful membership drives.

Believing “GLA” referred to a gay and lesbian association, Miguel inadvertently came out to Flatman, in one of the more unfortunate – and let’s face it – insensitive portrayals of gay characters in comics history. Thankfully, Marvel’s sensitivity to the need for more diverse representation in comics has increased exponentially in the years since Miguel’s outing, as has their ability to formulate accurate portrayals of LGBT characters. Having said that, let’s not forget that for every America Chavez or Northstar, there’s a Living Lightning hiding in the wings, shackled by outdated ethnic stereotypes and defined solely by his sexuality, rather than his strength of character.

8  Silverclaw

Like Triathlon, Silverclaw pounced forth from the imaginations of legendary comics creators Kurt Busiek and George Perez during their classic relaunch of the Avengers during the late ‘90s. And like Triathlon, she promptly faded into obscurity shortly after the titanic twosome left the series. Unlike Delroy Garrett though, Maria de Guadalupe Santiago has a much more direct link to the Avengers by way of their long-suffering butler Edwin Jarvis. Lupe was born in the fictional Central American country of Costa Verde, where she was initiated into the local mythology by her father.

After seeing her village on a television commercial for a children’s charity, Jarvis began sponsoring her upbringing at the local orphanage. Blessed with shapeshifting abilities that allowed her to assume the were-forms of numerous jungle beasts, Silverclaw is a formidable fighter who brings a versatile skill set to the table. Despite this, she’s remained sidelined for most of her career by more vibrant and relevant newcomers, little more than a forgotten utility player perpetually warming the bench.

7 The Shroud

Initially thought of as nothing more than a blatant ripoff of Batman or Daredevil or both, the Shroud has nonetheless managed to carve out a unique place in Marvel’s pantheon of heroes. Garnering a reputation for thinking outside the box, he proved his mettle to the Avengers by breaking into their West Coast compound. He joined the West Coast branch of the Avengers as an honorary member, only participating in a couple of official missions, preferring to wage his war on crime from the shadows (Duh!). For several years, he worked with a team of villains called the Night Shift, infiltrating the West Coast’s criminal underworld as one of their own.

He once again used unorthodox methods in a desperate attempt to locate his missing girlfriend, inhumanely using the villain known as the Owl to power a massive surveillance supercomputer. This led to a confrontation with Daredevil, prompting the Shroud to use his device to ruin ol’ Hornhead’s already shaky reputation. Despite the Shroud’s low blow, the two vigilantes teamed up to take down the Kingpin, freeing their captive loved ones and revealing Wilson Fisk’s vast criminal empire to the unsuspecting public.

6 Jack of Hearts

Despite a convoluted back story and a costume that somehow manages to be cool and goofy at the same time, this product of unbridled ‘70s wackiness still enjoys something of a cult following amongst discerning comic book aficionados. In 1976, Jack Hart first gained his powers and learned of his Contraxian alien parentage in, of all places, the pages of “Deadly Hands of Kung Fu.” Known primarily for his bad temper and unpredictable powers, Jack ran afoul of several established heroes before settling into the role of hero himself.

He served with the Avengers on several missions but continued to struggle with his ever-increasing powers. When it became necessary to isolate him for 14 hours a day, Jack decided to take his own life and detonated himself off-planet, taking a convicted child molester with him. For good measure, the Scarlet Witch brought him back to life to help disassemble her former team by blowing him up a second time. You can’t keep a good Contraxian down, though. Jack was last seen putting down a zombie invasion at Project PEGASUS, making short work of an undead Squadron Supreme and even getting the girl in the end.

5 Sandman

The Avengers have provided a home for many reformed villains over the years. Ever since the glory days of Cap’s Kooky Quartet, when three quarters of the team were former bad guys, villains have sought their path to redemption serving alongside fabled heroes like Captain America and Thor. Originally an immensely powerful Spider-Man foe, Sandman joined the ranks of the Avengers in an attempt to reform his criminal ways. During this tour of duty, Sandman proved to be an invaluable member of the team, playing a pivotal role in many adventures before a misunderstanding with Captain America led to a parting of ways.

Sandman eventually returned to his villainous roots but recently recalled his heroic days with the Avengers during Marvel’s AXIS event. Witnessing several of his criminal compatriots suddenly acting for the greater good, while under the influence of a personality inversion, Sandman stopped a prison breakout at Rykers Penitentiary. Unfortunately, despite his selfless actions, the media still pinned the breakout on the Sandman, the only villain of the bunch who was trying to do good of his own free will.

4 The Two-Gun Kid

Arguably the oddest entry on our list, the Old West gunslinger known as the Two-Gun Kid first encountered the Avengers during a tumultuous time travel caper involving their perennial nemesis Kang the Conqueror. Along with his contemporaries the Rawhide Kid, Night Rider, and Kid Colt, Matt Hawk unleashed frontier justice on all manner of evil and corruption in the American West. After hooking up with the Avengers, he became fast friends with Hawkeye, whose style of heroics he inspired and even joined the team in the present on many adventures.

When it was revealed he was stuck in continuity limbo, She-Hulk managed to negotiate his release but he was refused entry to his own timeline due to the temptation to set things “right.” He worked for a time as a bounty-hunter during Civil War, bringing in unregistered heroes, and also served in the 50 State Initiative before a Skrull ambush relegated him to the sidelines. Over the years, his inclusion amongst the ranks of the Avengers has become less an oddity and more of point of pride, with his long heroic legacy across multiple time periods spurring more than one modern to hero to action.

3 Moondragon

Bald is beautiful, as they say, and few come more bald or more beautiful than the alluring intergalactic telepath known as Moondragon. Another of the Avengers outreach cases, Moondragon has played the roles of both villain and hero throughout her long career. Her status as an Avenger is somewhat questionable thanks to her dubious moral code, which places her above her intellectual inferiors. She once took over an entire planet – including a besotted Thor – believing that the only way to achieve global peace was to take total control.

She also took the side of Korvac during his iconic battle with the Avengers, believing him to be of noble character for his desire to make the universe a better place through conquest. Later, she became corrupted by the insidious Dragon of the Moon, who sought her as a host on the earthly plane. With a track record like that, it’s a wonder she was given the time of day by her next team, the Guardians of the Galaxy. Although she participated in several missions with the Guardians, Moondragon didn’t make the cut for the team’s most recent incarnation and her current whereabouts are unknown.

2 Mantis

With a feature role in next year’s blockbuster “Guardians of the Galaxy Vol. 2,” don’t be surprised if – make that when – Mantis becomes a household name uttered from the lips of old and young alike. Although more recently connected to the Guardians, Mantis actually enjoys a long history with the Avengers and played an instrumental role in some of their most famous adventures. As the Celestial Madonna, her coming was foretold by the Priests of Pama, who had trained her since birth in preparation for her role as the mother of the Celestial Messiah. Her transcendence was an integral part of the Kree-Skrull War and the Avengers ongoing conflicts with Thanos.

Perhaps her most controversial involvement with the Avengers occurred during “The Crossing,” the same storyline that witnessed the murder of the Forgotten One. Returning to Earth as the evil bride of Kang the Conqueror, Mantis targets the Avengers for retribution, believing they facilitated the lie about her role as the Celestial Madonna. Thankfully, Kurt Busiek undid all of that unpleasantness during “Avengers Forever,” retconning this version of Mantis as one of the ever-handy Space Phantoms.

1 Nick Fury’s Avengers 1959

Dominic Fortune, Kraven the Hunter, Namora, Ulysses Bloodstone, and Sabretooth. Earth’s Mightiest…what? Criminals? Soldiers of fortune? Mercenaries? Certainly not “Heroes,” right? Call them what you will, when the chips were down, it was Nick Fury’s band of freelancers who put it all on the line when the world needed them the most. First appearing in “New Avengers” Vol. 2 #10, this Cold War incarnation of the Avengers bridged the gap between Fury’s time with the Howling Commandos and his recruitment into S.H.I.E.L.D.

Fury’s unlikely band of heroes cleaned up the remnants of the Third Reich in the years after World War II and revealed illuminating new details about characters such as Kraven and Sabretooth (who, it should come as no surprise, didn’t get along so well). Although largely forgotten in recent years, this intriguing collection of unsavory operatives brought a much-needed dose of pure adventure, adrenalin and unadulterated fun to a franchise that for a long time was anything but.

Did we forget someone who's unforgettably forgetable? Let us know in the comments who your favorite forgotten Avenger is!