Like the Avengers, the Guardians of the Galaxy in the comic books have always had a revolving door of superheroes who come and go. From the early team of the 31st Century (most of whom made their big screen debut in Vol. 2) to the modern comic crew that resembles its cinematic counterpart, fascinating heroes frequently sign on or at least offered aid to the Guardians. The Guardians of the Galaxy films, on the other hand, have positioned its characters as more of a family unit that's unlikely to break apart. They have, however, shown a willingness to add new good guys to the team.

The comics have a much richer tableau of dozens of characters who've served with or at least helped out the Guardians at one time or another. Across the 15 films Marvel Studios has produced thus far are a sizable roster of characters, both major heroes and sidekicks, any of whom could show up for a cameo or a larger role in a future Guardians movie — especially since Avengers: Infinity War will team the Guardians up with the Avengers for the first time.

It begs the question: who should be added to the cast in Guardians of the Galaxy Vol. 3? Read on to find out!

15. Hollywood

Despite the ridiculous name, this superhero and one-time member of the 31st Century Guardians of the Galaxy is actually a familiar face to hardcore Marvel fans. He was also slated to make a cameo in Guardians of the Galaxy Vol. 2 in the form of actor Nathan Fillion, but his scene was cut. His real name is Simon Williams, aka the modern superhero known as Wonder Man.

Simon is an actor who's been empowered by "ionic energy" to give him all sorts of superpowers, like flight, speed, strength, and so on. His power level is roughly on par with Superman, but he's never achieved anywhere near the kind of popularity as Krypton's last son.

One side effect of his powers is immortality; he doesn't age (though his hair eventually turns white), he doesn't eat or sleep, and he can't die. Thus, when the Guardians of the distant future encountered an older superhero calling himself "Hollywood," Vance Astro (see #5) recognized his voice as Simon Williams, having survived the wars that decimated Earth. Simon enjoyed a few stints with the Guardians as well as signing on with spinoff group the Galactic Guardians.

14. Angela

Angela's story is not just complicated, it's contentious. She debuted as a side character in Image Comics' Spawn, but she was created by Neil Gaiman, and it wasn't long before he and Spawn creator Todd McFarlane got into a legal spat about who owned the rights to the character. Gaiman won, and since he was returning to write for Marvel at the time, he decided to sell them the full rights to Angela.

In Spawn, she began life as an angel/bounty hunter working for Heaven, who later allied herself with Spawn. As ushered into the Marvel universe four years ago, Angela was reintroduced as "Aldrif," the long believed dead sister of Thor and Loki. She'd been taken from Asgard by the realm of "Heven," but returned thanks to some universe-altering hoo-doo.

Guess who the first people were that Angela met upon entering the Marvel universe? The Guardians of the Galaxy. After a brief fight, she wound up joining the team. Her powers include the same basic set as her brother Thor's, though she can fly without the need of a magic hammer.

13. Talon

He looks like a feral alien, but Talon is actually an Inhuman of the distant future. In the 31st Century, Inhumans were made slaves, but Talon managed to escape his captivity with the help of sorcerer Krugarr (see #10). Talon also possessed some natural talent with magic, and agreed to become Krugarr's apprentice for a time, but eventually left to join the Guardians.

Talon is a fun character because he's relentlessly upbeat and always at-the-ready with a sarcastic comment. He also vaguely resembles Lion-O from Thundercats, and who wouldn't want to see that in Guardians of the Galaxy? Plus, Inhumans are kind of a big deal at Marvel these days, so... Hello, corporate synergy!

His abilities include enhanced strength, reflexes, and speed, but most interesting are his claws. Talon can actually shoot his claws at high speed, effectively giving him five bullets on each hand. He regrows new claws instantly, making his fingers semi-automatic!

12. Bug

A native of the Microverse and a major player in the Micronauts series of the '70s and '80s, Bug is an alien "insectivorid" from the planet "Kaliklak" (yes, seriously). What makes him unique amongst his species are his skills as a thief and his upbeat personality. Like his namesake, he has incredible agility, balance, and reflexes. He also possesses enhanced speed, strength, health regeneration, and more.

After countless adventures in the Microverse — and let's face it, Marvel's not likely to bring that to a big or small screen anytime soon — Bug was recruited to join the Guardians of the Galaxy to fight the Badoon in the present. Afterward, he stayed on the team through many more exploits. Following the invasion of the Cancerverse, Bug left the team to return home to the Microverse.

In the movies, his quirky nature and oddball appearance would only add to Guardians of the Galaxy's charms.

11. Silver Surfer

This one's a total pipe dream. The rights to Silver Surfer are still owned by 20th Century Fox, because he's considered a Fantastic Four character. But since it's clear that Fox hasn't the slightest idea how to make a good F4 movie, the chances are growing daily that Marvel will regain the rights to its premiere super-family.

Whenever it happens, getting access to the Fantastic Four catalog would give Marvel back the rights to all sorts of cool and important characters, including Doctor Doom, Galactus, and everybody's mercurial space wave-rider. While he's never been a full-blown member of the Guardians, Silver Surfer has crossed paths with the team on several occasions in the comics.

Most fans agree that one of the few things Fox did well was cast Doug Jones as the Silver Surfer. While it's a given that Marvel would want to recast the part to set their Surfer apart, Jones' work was memorable enough that audiences probably wouldn't require a full-blown introduction to who and what the character is.

10. Krugarr

Krugarr is a member of an alien species called the Lem. Looking like a cross between a dragon and a worm, Krugarr was an ally of the original team, the 31st Century Guardians.

This is because one thousand years in the future, Krugarr is the Sorcerer Supreme. You'd imagine that there were dozens of Sorcerers Supreme between the time of Doctor Strange and Krugarr, but you'd be wrong. Krugarr was Strange's immediate successor, while Strange himself moved up to become the Ancient One, his physical body having been killed long ago by Dormammu.

Like all good sorcerers, Krugarr is highly skilled in the mystic arts, and he aided the 31st Century Guardians many times in their adventures, including one particularly brutal fight against Dormammu. Introducing him to the Guardians of the Galaxy movies would require some rejiggering — having two Sorcerer Supremes at the same time would violate the magical order of things — but he's a selfless, fearless hero. And more alien diversity never hurt anybody.

9. Quasar

Daughter of a Kree father, Captain Mar-Vell (seriously), and an Eternal named Elysius, Phyla-Vell was sort of accidentally brought into being when reality was destroyed and then rebuilt. She wields the Quantum Bands of the former Quasar, Wendell Vaughn, which give her the ability to absorb and redirect energy. She also has a powerful sword that she uses in battle.

Phyla is a talented warrior, and has the distinction of being one of the few superheroes to have ever bested Ultron. Not far into her career, she teamed up with Moondragon (see #7), and the two became inseparable. They later became lovers as well as cosmic crime-fighting partners.

Phyla-Vell joined the Guardians of the Galaxy after a universe-spanning crisis, but the death of Moondragon compelled her to make a deal with a personification of death to bring her back to life. Unfortunately, the deal effectively turned Phyla evil, creating a rift with her fellow Guardians. It ended with her death at the hands of Thanos.

8. Captain Marvel

Brie Larson is set to join the Marvel Cinematic Universe in its first female-centric solo flick, Captain Marvel, in 2019, but prevailing rumors suggest that she might show up much sooner, as in Avengers: Infinity War.

Captain Marvel, from the character's roots as the Kree warrior Captain Mar-Vell to his successor Carol Danvers, has always had a more cosmic focus than other members of the Avengers. While Danvers' Captain Marvel has remained a little more rooted to Earth, she's spent plenty of time in space, too. So putting in an appearance with the Guardians of the Galaxy wouldn't require a big leap in logic.

It's not without comic book precedence, either. Carol has helped out the Guardians before, usually in situations too big for the Guardians to handle alone. Her powers come from exposure to Kree technology, which gave her flight and strength, and more importantly, the ability to absorb any power sent her way — from energy blasts to fisticuffs — store it as kinetic energy, and then send it back at her enemies.

7. Moondragon

In the movies, Drax's origin has been drastically altered from the comics. There, he was once a human named Arthur Douglas who was killed by Thanos on Earth along with his family. Thanos' father Mentor transferred Arthur's consciousness into a powerful new body, and Drax the Destroyer was born. Seeking revenge on Thanos was his sole purpose. In the films, meanwhile, Drax is from a primitive alien culture, and his family was murdered not by Thanos, but by Ronan.

In the comics, Arthur Douglas had a daughter named Heather who survived Thanos' attack, unknown to anyone. She was taken in by Mentor and trained as a warrior, where she learned powerful psychic abilities. She adopted the name Moondragon and spent years, like her father, hunting Thanos before joining the Guardians.

The movies' version of Heather is Drax's daughter Kamaria, who's never been seen (and as far as we know, is dead). But it wouldn't be a huge leap for her to show up in the films as Moondragon — and seeing Drax as a family man would give his character added depth. Moondragon's relationship with Drax would also fit perfectly with the films' focus on the Guardians as a dysfunctional family unit.

6. Nova

2014's Guardians of the Galaxy already introduced us to the Nova Corps and their home planet Xandar. Nova was the last member of this league of space police, taking on cosmic superpowers when he donned a special helmet.

Nova has taken on new popularity in the comics the last few years, thanks to the introduction of a new Nova, a teen named Sam Alexander. It took Sam a while to learn the ropes, and balancing superhero life with teenage angst is never easy. But he was an Avenger not long ago, alongside other teens like Kamala Khan (Ms. Marvel) and Miles Morales (Spider-Man), and he remains active among the young superhero community. So it's only a matter of time before this increasingly important character makes his way to the big screen.

Given their focus on space-based adventures, Guardians of the Galaxy seems like a perfectly logical place for either version of Nova to make his debut.

5. Major Victory

Like the man he idolizes, Vance Astro is a man out of time. A millennium out of time, to be exact. Sent into deep space in the 20th Century, he awoke from cryogenic sleep one thousand years later to discover that human technology had progressed far past him during his slumber, and that he and his mission were now obsolete.

At least he had the Badoon occupation of the solar system to take his mind off matters. He teamed up with the likes of Yondu, Charlie-27, Martinex, and Starhawk to take on these lizard-like aliens, and then explore the galaxy. Years later, he changed his superhero name to Major Victory and took his Captain America obsession to the next level, acquiring Cap's shield and wearing a uniform modeled after him.

While several of those original Guardians show up briefly in Guardians of the Galaxy Vol. 2 (as Ravagers, not heroes), their longtime leader and stalwart moral compass Vance Astro was not among them. Time travel has brought him back in time more than once to meet other Marvel heroes and modern Guardians, so this important character is overdue for his spotlight.

4. Valkyrie

In Viking mythology, valkyries were heralds who roamed battlefields, finding the souls of the dead and guiding them to Valhalla, aka Heaven. In Marvel Comics, Valkyrie is an Asgardian named Brunnhilde, chosen by Odin for this important task and given elevated strength and abilities.

Her history is far too convoluted to tell here; suffice it to say, she's had it rough, her soul having repeatedly been forced to hop from one mortal body to another, never finding peace. She's served with the Secret Avengers and the Defenders, and she's been Thor's lover at least once.

Valkyrie's story looks to be drastically reinterpreted in Thor: Ragnarok, with the Asgardian warrior apparently serving the Grandmaster, bringing him "contenders" for his battle arena. But don't be surprised if encountering Thor brings her back to a more heroic purpose. And with her already living out among the cosmos — and Thor himself unlikely to last much longer, with Chris Hemsworth's contract on the verge of expiring — she could be a fun addition to the Vol. 3 cast.

3. Cosmo

How can you not love a dog with incredible mind powers and a thick Russian accent? Cosmo was a 20th Century canine sent into space by the U.S.S.R.'s space program before humans were allowed to travel beyond the atmosphere. Believed lost, Cosmo resurfaced years later in deep space having mutated superpowers from the ravages of radiation.

He's now a fully self-aware individual with a strong moral compass who serves as chief of security on the space station Knowhere and speaks via telepathy. In the comics, Knowhere was the Guardians' base of operations for a while, and when Star-Lord and his pals were out on missions, Cosmo watched over their home and liaised with them, providing intel when needed.

Cosmo was briefly glimpsed in the first Guardians of the Galaxy movie as one of the rarities owned by the Collector; he walked by in the post-credits tag as well. One would imagine that he didn't get a bigger role because the filmmakers thought that having two talking, anthropomorphic animals (counting Rocket) might be too much. But Cosmo plays an important part in the comics, so it's definitely time for him to enter the mix.

2. Heimdall

Didn't see this coming, huh? And yet, when you think about it, it makes so much sense.

First, for countless ages, Heimdall has been Asgard's guardian, stationed on the Bifrost to defend his people from any and all intruders. But if the trailer for Thor: Ragnarok is any indication, he may be a free agent in the near future, without a kingdom to defend.

Second, it has happened in the comics. In an issue starring the 31st Century Guardians, Heimdall spent time in captivity alongside Aleta, aka Starhawk at the time. The two commiserated over their joint suffering to the point that they developed feelings for one another. Heimdall has also appeared on Disney's Guardians of the Galaxy cartoon.

Lastly, it's Idris Elba. Not only is he one of the most criminally underused actors on Marvel Studios' roster, he's a highly respected actor on the cusp of super-stardom. And his ultra-serious tone as Heimdall would give Guardians of the Galaxy something it's lacked from the start: a straight man. The one team member who isn't afraid to comment on just how insane it is for a bunch of misfit screw-ups to save the galaxy.

1. Adam Warlock

This one's a no-brainer — especially since his coming has been teased in both Guardians films. Adam Warlock is a "perfect" human specimen created by a group of evil scientists as the intended first member of a superior human race. But his perfection gave him a conscience, and he rejected his creators' plans.

Adam has the kinds of powers you'd expect: speed, strength, flight, energy manipulation, and more. He's also been in possession of the soul gem at times, one of the six Infinity Stones Thanos is after, and intriguingly, the only one currently unaccounted for in the MCU. There aren't a lot of superpowers amongst the Guardians — Groot is pretty much the only one with outside-the-norm abilities — so Adam's presence could give the group a much-needed power boost.

Adam Warlock teamed up with the Guardians on multiple occasions in the comics and even became a card-carrying member at one point. Adam also has the distinction of being the first human to wield the Infinity Gauntlet, which he did to set right all the things Thanos messed up when he had it. This has led to speculation that Adam might show up before Vol. 3 — as in, in Avengers: Infinity War — and that the post-credits Vol. 2 scene was teasing that more than Vol. 3.

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What other Marvel characters would you like to see join the Guardians of the Galaxy in the third big screen adventure? Let us know in the comments.