A hero’s rogues gallery is a huge factor in why readers come back for more, as the quality of the villains and the ways in which they make the hero’s life difficult lend to the ever-needed growth of said hero. In “Invincible,” written by Robert Kirkman and illustrated by Cory Walker and Ryan Ottley, Mark Grayson -- better known to the world as Invincible -- has a unique and large cast of enemies.

RELATED: 15 Most Insane Moments From Invincible

In the list below, you’ll find a mix of foes from all over the villainous spectrum: some pure evil, some not always bad, some downright repentant; others, meanwhile, simply love to fight. Whatever the case may be, check out Invincible’s top 15 formidable foes below!

SPOILER WARNING: The following article contains spoilers for the "Invincible" comics series.

15 BATTLE BEAST

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The scourge of twin galaxies; the conquerer of a thousand worlds; the name that makes galactic empires tremble: Battle Beast. While Battle Beast certainly falls in the category of villain-turned-ally, his allegiance towards anyone serves mainly to benefit himself. See, Battle Beast is on a never-ending quest to find challenging opponents to fight.

When Machine Head -- the leader of the villainous team, The Order -- recruits Battle Beast in issue #19, he is tasked with fighting alongside other members of the organization in order to defeat Invincible and Titan. Battle Beast’s main reason for joining the team is to test out his fighting capabilities against the heroes of Earth; so, just as Machine Head uses him for personal gain, he likewise takes advantage of Machine Head as a means of satisfying his blood lust. While he is defeated by the duo, it is not the last time Battle Beast is seen, as he plays a huge role during the Viltrumite War (issues 71-78), fighting alongside the likes of Invincible, Omni-Man, Tech Jacket and Allen the Alien.

14 DOC SEISMIC

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Invincible has certainly battled his fair share of duds, especially early on in his career; but every superhero needs to start somewhere, right? Introduced in issue #10 of the series, Doc Seismic – an average sized person with no apparent superpowers of his own – can create earthquake-like events with the dual gauntlets he wears. In their first encounter, Doc Seismic attempts to destroy Mount Rushmore, but is thwarted by an inexperienced and eager Invincible.

While never becoming much of a threat to Invincible, Doc Seismic is one of those villains who never seems to go away (as with many of Invincible’s rogue gallery). In the fourth issue of “The Pact, Volume 2,” by Robert Kirkman and Jason Howard, it’s discovered that Doc Seismic is leading a group of lava monsters known as the Magmanites; but this doesn’t last long, as he’s swiftly defeated by Invincible and brought to prison. In issue #106 of “Invincible,” Doc Seismic is recruited by Volcanikka, another lava-like creature, who turns him into one himself. And finally, in a very offhand way, Robot kills (or so it seems) Doc Seismic in issue #113. Just as he’s brought in as a mediocre villain, he exits the series in mediocre fashion.

13 MAULER TWINS

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Imagine creating a clone of yourself, only for the clone to believe that it is the true you. This is exactly what happens when the original Mauler Twin (no one really knows which one is which) decides to test a cloning machine on himself. Two of Invincible’s oldest enemies, the Mauler Twins first appear in issue #2 of the series, written by Robert Kirkman, with illustrations from Cory Walker.

While possessing super strength, they are no match for Invincible in their first encounter with him. Trying to steal video game systems for spare parts for the robots they’re building, a costume-less Invincible -- actually, he’s only wearing underwear -- is able to quickly take them out. As with many of the villains in Invincible, though, the Mauler Twins return on numerous occasions, sometimes with plans of their own, but mostly as pawns in a grander scheme, orchestrated by a fiercer enemy.

12 THE LIZARD LEAGUE

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The Lizard League is a super powered terrorist group consisting of members King Lizard, Iguana, Salamander, and Komodo Dragon. First appearing in issue 9, the League tries to poison the city’s water supply, but they are easily apprehended by Invincible and Atom Eve (more so Atom Eve).

Eventually, the League escapes prison in issue #38. Taking control of a nuclear missile silo, the group becomes engaged in a battle with Rex-Splode, Shrinking Ray, and Dupli-Kate (as Invincible is in space fighting the Sequids). In a much more successful fight, the battle actually becomes quite deadly, as Komodo Dragon uses his enhanced strength to kill both Shrinking Ray and Dupli-Kate (though it turns out it was only her clones); however, Rex-Splode somehow manages a killing spree of his own. After taking out Salamander and Iguana, and just before Brit shows up and King Lizard is seized once again, Rex-Splode shoves an explosive in Komodo Dragon’s mouth, but not without losing his own hand to the blast in the process. While they didn’t fair too well against Invincible or Atom Eve, it’s always shocking when a villain kills a hero -- and the League of Lizards (Komodo Dragon, anyway) -- manage to brutally murder two.

11 D.A. SINCLAIR

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Some of the villains on this list start out as foes of Invincible, but then, in their own rights, become allies. D.A. Sinclair is one such enemy. In issue 20 of Invincible, Sinclair is introduced as a college classmate of Mark Grayson; however, he uses his superior intelligence to create zombie-like cyborgs, known as the Reanimen. Sinclair even turns another college student, Rick Sheridan, into one before Invincible is able to capture him.

Once turned over to Cecil Stedman -- Invincible’s government handler -- Sinclair is actually offered a job, putting his smarts to work for the betterment of humanity. First, Sinclair uses the bodies of fallen soldiers to create new Reanimen, but after the Invincible War (a literal war with a whole bunch of Invincibles from alternate dimensions), he’s tasked with creating superpowered Reanimen from the corpses of the dead Invincibles. While his skills are meant to help, what makes Sinclair so scary is his intelligence, and the simple fact the he is just so freaking creepy any time he shows up.

10 SEQUIDS

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In issue 18, on a trip to Mars accompanied by Invincible, a group of astronauts including a man named Rus Livingston come across not one, but two alien races -- Martians and Sequids. The Martians had enslaved the Sequids -- a mindless race -- for thousands of years. Now free, the Sequids pose a threat to the entire universe for the injustices done to them. In an effort to prevent the humans from being taken over by the Sequids, the Martian army plans to execute the astronauts. Running for their lives, the men quickly secure themselves in their shuttle and take off -- accidentally leaving Rus Livingston behind.

Now fully controlled by the Sequids, Rus Livingston returns in issue #38 for a five-issue arc as a conduit for the creepy, crawling creatures, bent on the destruction of Earth. What ensues is a battle across the world and space, as Invincible leads a team of heroes to stop the aliens without being controlled themselves. Making a few more appearances throughout the series, the Sequids might be a thoughtless race until they latch onto a host, but they’re quite determined in righting the wrongs done to them -- an extremely dangerous prospect.

9 FLAXANS

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The Flaxans -- a highly advanced, warrior race from another dimension -- are first encountered by Invincible and his father, Omni-Man, in issue #3. During their engagement, Omni-Man is taken through the Flaxan portal to their world. What they don’t realize at the time, though, is that in the Flaxan dimension, time moves at a rapid pace: years to the Flaxans are mere seconds to humans. In issue #4, after just a few days, Omni-Man returns, but he tells Mark that the Flaxans had enslaved and tortured him for months on their planet. Able to escape, but massacring their military in the process, the two are not sure if they’ll ever see the Flaxans again.

Invincible and other heroes battle the Flaxans six more times as they try to attack Earth, having spent hundreds of years in their dimension studying Omni-Man’s costume and preparing to destroy him. Due to their ability to grow as a race much quicker than humans, no one can ever know if or when they’ll return to seek revenge again -- or how strong their military will be if they do, making the Flaxans a frightening threat.

8 DINOSAURUS

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To challenge Invincible both physically and ideologically means that the villain must not only have strength, but conviction. In the case of Dinosaurus -- who made his debut in issue #68 -- it takes Invincible some time to discover how delusional the beast truly is. When David Anders stops caring about important topics, he transforms into Dinosaurus. When in Dinosaurus form, Anders’ goals depend on the principles he holds dear at the time. For instance, his idea that leaving a city destroyed (after the Invincible War) rather than the heroes rebuilding it, will help to stimulate the economy; or the concept of destroying Las Vegas (issues #97-100) with multiple bombs, as he believes that it has become a man-made cancer on a once, naturally beautiful desert.

Invincible struggles with Dinosaurus’ ideas, as he sometimes agrees with them. Ultimately, Invincible is forced to take him down, particularly when one bomb detonates in Las Vegas, killing countless people, and turning the city into glass. What makes Dinosaurus different from most villains, however, is his ability to participate in logical, even philosophical conversations with Invincible -- ultimately leading to the realization of his massive errors, and his request for death at the hands of Invincible.

7 ALTERNATE INVINCIBLES

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In various alternate dimensions, a version of Mark Grayson exists. The majority of the other Marks are evil, having either been raised by their Viltrumite fathers to take over Earth, or merely out of a lust for power. The first alternate Invincible is shown in issue #16 on a large screen in the middle of a city, explaining his takeover of the world. This also serves as an introduction to Angstrom Levy, a prominent antagonist of the main Earth’s Invincible.

After believing he’s killed Angstrom Levy (more on this later), Invincible is shocked to discover a small army of other Invincibles attacking Earth in issue #60. Not only is Invincible joined by his usual partners, but much of the longstanding Image Comics roster join the battle as well, including Tech Jacket, the Capes, Dynamo 5, Spawn, Youngblood, Cyberforce, Savage Dragon and more. The actual battle only lasts one issue, but it’s not the last time Invincible has to survive his counterparts, as he’s thrust into another dimension in issue #103 and pitted against the deadliest, most maniacal (and cannibalistic) versions of himself to date.

6 ROBOT

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While some entries in this list include villains-turned-allies, Robot is quite the opposite. A leading member of the Teen Team, Robot meets Invincible for the first time in issue #2, and they become fast friends. As time goes on, Robot becomes not only more technologically equipped, but emotionally and ideologically changed after having fought, and then ruled, the Flaxan Empire for decades.

Shortly after his return to Earth, his true motives are revealed in issue #108. Robot plans a swift and hostile takeover of the world -- meaning killing any heroes who get in his way (and there are many), as well as decisively snuffing out any threat to the world, sometimes before it can even act. Initiating this plan with a robot army of his creation, there is really no one in the universe who can stop him; not even Nolan and his Viltrumite followers. The only way for Invincible to continue on living, is to leave the world he knows with his family, and get as far away from Robot as possible. While Robot believes that what he’s done thus far has produced more good in the world than ever before, Invincible remains unconvinced.

5 THRAGG

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The Viltrumites are a human-like, all-conquering, warrior race -- the most feared in the known galaxy, and for good reason. Possessing uncanny strength and speed, they believe themselves to be the superior race. A thousand year-old Viltrumite -- having fought in the Viltrumite civil war -- Thragg not only enters the “Invincible” universe in “Invincible Returns" #1 as the Grand Regent of the Viltrum empire, but as quite possibly the strongest member of his species.

During the Viltrumite War, as The Coalition of Planets’ team of fighters (Invincible, Omni-Man, Allen the Alien, Oliver Grayson, Battle Beast, Space Racer, Thaedus and Tech Jacket) do more harm to the Viltrumite empire than expected, Thragg takes it upon himself to lead the surviving members of his race. In the process, he single-handedly kills the Coalition’s founder, Thaedus, puts Oliver (Invincible’s younger brother) into a coma, and severely injures both Mark and Nolan. Eventually, Thragg is overthrown by Nolan and the remaining Viltrumites, and exiled for his crimes; but in recent issues, he’s been creating an army of half-Viltrumite children all across the galaxy, taking over various worlds and increasing the size of his new empire -- presumably for a hostile final war.

4 ANGSTROM LEVY

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With the power to travel between alternate Earths, Angstrom Levy is fully aware about the threat of Invincible in most dimensions; however, when introduced in issue #16, he doesn’t care much for killing Invincible, but rather, he wants the memories of all different versions of himself in order to move more freely through the parallel worlds. Enlisting the help of the Mauler Twins to create a machine that would give him the abilities he desires, Levy tries to abruptly stop the memory transfer process when Invincible shows up and the twins almost kill the hero. Unfortunately for Levy, during the shutdown, the machine explodes, causing severe external and internal damage to his body. And who does he blame for his life-altering circumstances when restored with a new body? Invincible, of course.

Now bent on revenge, Levy uses his portal-opening device on two different occasions to take Invincible’s mom hostage (issues #32-33) and then a pregnant Atom Eve (issue #103). The extremely personal touch to their feud makes Angstrom Levy one of Invincible’s greatest foes, as he’s one of the few enemies who can make Invincible snap into a rage-filled berserker without much effort.

3 CONQUEST

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In the moments following the Invincible War in issue #61, Conquest appears on Earth and confronts Invincible. Sent by Grand Regent Thragg to take over Earth, Conquest is a fierce and intimidating Viltrumite, who is quite experienced in the hostile takeovers of planets. Giving Invincible an ultimatum -- join in conquering Earth, or die and Conquest will do it himself -- Invincible goes on the offensive immediately. What ensues is a devastating and vicious battle taking place on the pages of three issues, that causes more destruction than the whole Image universe fighting against the evil Invincibles did. It also causes the death of Atom Eve (or so Invincible thinks), due to Conquest punching a hole through her stomach.

Having been defeated by Invincible during their first battle (when Mark takes things personally, there’s no stopping him), the two have one final battle during the Viltrumite War, with Invincible coming out as the victor. This time, he kills the villain once and for all. But the overall brutality of their battles makes Conquest one of Invincible’s most incredible antagonists.

2 ANISSA

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The next entry on this list is such a devastating character in Mark’s life, not because of her physical strength, but because of something much more. Anissa is a Viltrumite who actually visits Mark in issue #37, well before Conquest, trying to reason with him in regards to the Viltrumite takeover of the planet; but when he won’t listen, she first fights him and then prepares the way for Conquest.

Later in the series, after Nolan has taken control of the Viltrumite empire (or what’s left of it), Anissa is tasked with living amongst humans in secret. But after multiple flirtatious encounters (on her part, as Mark is in love with Atom Eve and they’re having a child together), Anissa confronts him in issue #110. As they battle in the sky, she overpowers him, and in a very shocking and disturbing scene, sexually assaults Mark. This causes Mark an overwhelming amount of grief and self-blame, ensuring a heartbreaking time in Invincible’s life, and making Anissa one terrible and disgusting foe.

1 OMNI-MAN

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Nolan Grayson, created by Kirkman and Walker, is introduced in the very first issue of “Invincible” as the famous Omni-Man. While he’s certainly an ally of Invincible in the later issues of the series, what makes him such a dreadful villain is who he is personally to the titular hero: his dad.

After discovering his father killing The Immortal (for the second time) in issue #10, Nolan tells Mark about his Viltrumite heritage, and why he’s really on Earth: to take it over and prepare the way for it to become a Viltrumite breeding ground. While Nolan claims to actually love Mark and his mother -- which were never his intentions or orders -- Invincible is too shocked, angry and sad to care. With that, Invincible and Omni-Man fight, or more accurately, Omni-Man beats the crap out of his own son with ease, and then leaves the planet instead of killing him. A crushing blow, not just physically, but emotionally, Omni-Man’s betrayal causes Invincible to have to prove himself as his own person/hero, while carrying the weight of the world on his young and inexperienced shoulders.

Who do you think is Invincible's most brutal foe? Let us know in the comments!