Despite the fact that the plots of the games usually appear barebone, ''VideoGame/MetalSlug'' has its fair share of characters, all of whom have a great deal of backstory to them. The backstory to each character is where the real plot points stand out.

!Protagonists (Broken down by game appearance)

!!Metal Slug

[[WMG: Marco (Marchrius Dennis Rossi)]]

Marco joined the military's vocational school following technical high school, and after graduating, joined the Peregrine Falcons Squadron, soon becoming its leader. Though generally a good-natured guy, he tends to flip his shit whenever Morden is mentioned, given the fact that Morden was responsible for the deaths of many of his good friends.

Off the battlefield, Marco is an expert computer technician, often creating computer viruses for fun, but one in particular that unintentionally made its way onto the net infected the military's mainframe, made it past all of the firewalls and almost caused the launch of several nuclear missiles. He intends to take that secret to his grave.

From Metal Slug 6 onward, Marco's unique ability is to deal double damage with his handgun. If playing on Easy, though, this ability transfers over to the automatic Heavy Machine Gun. In Metal Slug 7/XX, he can also use the Burst Shot, which allows for rapid fire, though he can't move.

!!Marco Rossi's Tropes:

%%* TheAce
* AllAmericanFace: More or less designed as the typical American war movie hero.
* {{Badass}}: He is essentially a one-man army, killing soldiers, zombies and monsters as if they were nothing.
* BerserkButton : Anything involving General Morden.
* BoringButPractical: His ability in the later games is dealing double damage with a handgun. While this is hardly flashy, it's invaluable whenever you're without any upgrades. In ''Defense'', his special is to shoot his Heavy Machine Gun, which is hardly flashy but a good all-purpose skill.
* EagleLand: He's a tanned, blonde-haired American who loves big guns and justice.
* EmergencyWeapon: Starting in ''6'', he is focused on making the starting peashooter of a handgun not so pathetic. By dealing double damage, it's actually pretty decent. Another weapon is still preferable, but not as much.
* ExtendoBoxingGlove: An alternate melee attack for when he's crouching.
* {{Handguns}} : His attack power is doubled while firing a handgun.
* TheHero: The leader of the team and the poster boy of the series.
* HeterosexualLifePartners: With Tarma, who has been with him since the very beginning.
%%* NiceGuy
* OpenSaysMe: An alternate melee attack when he opens chests is to simply kick them open.
* PlayfulHacker : During his spare time. He accidentally almost launched nuclear weapons at one point.
* TheSmartGuy: Outside the battlefield he's an expert hacker.
* VitriolicBestBuds : With Tarma
* WeaponOfChoice: The Heavy Machine Gun.

[[WMG: Tarma (Tarmicle Roving III)]]

Son of a military man, he entered the Special Forces Training School after finishing junior high. At age 20, he joined the Peregrine Falcons on a mission to rescue the president, at which point he met Marco, the two becoming fast friends. When he found out Marco had been selected to take part in the counteroffensive against Morden, Tarma was quick to volunteer. Though he often pokes fun at Marco, he holds his friend in the highest regard.

Whenever he's not engaged in battle, he builds custom motorcycles with such attention to detail that he puts most professionals to shame. If and when he can retire from active service, he intends to open his own motorbike shop.

Tarma's engineering skill from Metal Slug 6 onward allows him to make better use of the Slugs that he comes across. They can take twice as many hits, he can use the vulcan fix, the vulcan's damage is increased, and he obtains twice as many Slug Shells on pickup. In 7/XX, he can also kick Slugs, which can either recover or damage them. However, the double durability and recovery/damage kick only works on Vehicle Slugs.

!!Tarma Roving Tropes:

* AcePilot: His specialty on the team starting in ''6''. He's the best at handling vehicles and it translates to gameplay as tougher vehicles, stronger weapons in them, and new abilities.
* BadassBiker: Off-screen. The CoolShades and his backstory of expertly building bikes establish him as this.
* CoolShades: Never seen without his shades. It also helps distinguish him from Marco at a glance.
* EverythingsBetterWithMotorcycles : His hobby in his spare time.
* GadgeteerGenius : He's the team's Slug expert, largely due to him tinkering with vehicles in his spare time.
* GlassCannon: In ''Defense'', he has the lowest HP of the four main characters but his Shotgun does the most damage.
* HeterosexualLifePartners: He's the only character who has been with Marco from the beginning.
* MeaningfulName: As the Metal Slug technician of the team, his name last name is ''Roving.''
* TheLancer: Marco's best friend and foil, as well as the default player 2.
* PercussiveMaintenance : His Slug Kick. Sometimes averted, causing damage to the Slug instead.
* VitriolicBestBuds : With Marco.
* WeaponOfChoice: The Shotgun.
!!Metal Slug 2

[[WMG: Eri Kasamoto]]

Eri was found abandoned on the steps of a church. When she became wise to the ways of the world, she eventually ran off and became the leader of a gang of street kids. The Intelligence Department of the Regular Army noticed her leadership skills, and thus recruited her. She went on to receive spy training, and took part in a number of missions requiring assassination. She found these types of missions distasteful, and requested a transfer to the SPARROWS division. Given her impressive track record, it was approved. Once transferred to the SPARROWS division, she was assigned the role of team demolitions expert.

Given Eri's background of growing up among street children, her demeanor and attitude in life mostly boils down to "Rely on nobody but yourself."

Eri's unique talent from Slug 6 onward is handling grenades. She starts each life with 20, gains double grenades on pickup, deals more damage with them, and is the only one able to aim her throws, which includes straight upward.

!!Eri Kasamoto Tropes:

* ActionGirl: Kicks as much ass as any of the men.
* {{Badass}}: She is just as powerful as her male counterparts.
* BareYourMidriff: Setting a trend, her military "uniform" exposes her belly.
* TheBigGirl: While the whole team packs plenty of power, she's the explosives specialist.
* DarkAndTroubledPast: We need to reiterate that her old career as an espionage agency assassin was somehow so "distasteful" that she compared it unfavorably to ''blowing people up with grenades and flamethrowers''.
* HeterosexualLifePartners: With Fio.
* InformedLoner: She's on a four person team by the time of her introduction and does little to show off her loner personality.
* {{Mukokuseki}}: While she does have (light) brown eyes, her hair's a shade of blond that is anything but Asian, let alone Japanese (she's from Hiroshima).
* StuffBlowingUp: Starting in ''6'' her specialty is grenades.
* TomboyAndGirlyGirl: Eri's the Tomboy. Her backstory, attitude, and appearance are much tougher than Fio's.
* WeaponOfChoice: The laser.

[[WMG: Fiolina "Fio" Germi]]

Daughter of the massively wealthy Germi Family, hailing from Italy. The Germi family has historically been a military family, sending their oldest into service, so naturally her father wished for a healthy son to carry on the name. However, following Fio's difficult childbirth, her mother was unable to bear anymore children, making it the first time the Germi heir was female.

Eri's polar opposite, Fio was raised in a loving family, and has a cheerful and upbeat demeanor. Aside from her soldier training, she also studied chiropractics, acupuncture and moxibustion in university, and hopes to become a sports doctor in the future.

Fio's special trait from the sixth game onward is carrying extra ammo for her weapons. She starts each life with a Heavy Machine Gun, and gains 50% more ammo on weapon pickup. If playing on Easy, though, she automatically gets the Big Heavy Machine Gun as her initial armament.

!!Fio Germi Tropes:

* ActionGirl: No less a capable fighter than any of the men.
* BadassAdorable: Best exemplified by her victory animation of her falling down coquettishly. Mind you, this is after wiping out hundreds of enemy troops.
* BareYourMidriff: As is the norm with female fighters in the ''Metal Slug'' universe.
* TheChick: The medical expert of the team and also the most emotional.
* GuestFighter: She is playable in ''VideoGame/TheKingOfFighters: Maximum Impact 2''.
* HeterosexualLifePartners: With Eri.
* {{Meganekko}}: An archetypical example in video games. She's got the cute look, modest personality, and is overall moe because of it.
* MissFanservice: A lesser one compared to Sofia, but far better known among fans. Cute girl with with a nice figure (which is obvious on any piece of official art, especially next to the modestly endowed Eri).
* MoreDakka: Her Specialty from Metal Slug 6 onwards. The Heavy Machine Gun is basically her ''default'' weapon.
* SmallGirlBigGun: The heavy weapons specialist is the smallest of the four main playable characters.
* TookALevelInBadass: She's normally the meekest of the main cast, but at the end of Metal Slug 3, she stands in a very proud manner atop of a floating Metal Slug. Eri, in comparison, has a hunched demeanor.
* TomboyAndGirlyGirl: Fio's the Girly Girl compared to Eri's Tomboy. She's got a sheltered background, [[{{Meganekko}} cuter looks]], and is much less hardened in general.
* WeaponOfChoice: The Rocket Launcher.
!!Metal Slug 4

[[WMG: Nadia Cassel]]

Initially, Nadia wanted to go into the modeling business, but she couldn't stop eating, which meant she kept gaining weight, so she enlisted into the Regular Army for the exercise. Here, she discovered her skills as a soldier, and was chosen to help in stopping the Amadeus Syndicate from releasing its supervirus. Here, Nadia was a stand-in for Eri, who had been assigned to other duties. The one thing putting her apart from Eri is that her alternate melee weapon is a souped-up taser, capable of shredding the enemy. Unfortunately, due to some in-game bugs, she doesn't get as many points for using her melee.

!!Nadia Cassel Tropes:

* ActionGirl: Runs and guns with the best of them.
* BareYourMidriff: Not standard attire in the military, but no one's complaining.
* BigEater : The reason she joined the military is to lose weight. That's right, joining the military during a conflict seemed like an easier way to lose weight versus eating less.
* FormerlyFat: Well, except the ending has her eating a big feast alongside the other heroes.
* GaulsWithGrenades : She's French. Her art in ''VideoGame/MetalSlugDefense'' even has her posing with a pair of grenades.
* GirlishPigtails: As evidenced by the fact she joined the military not to prove herself, defeat evil, or a love of fighting, she's just a girly girl who joined for girlish reasons. Her hair is appropriately in pigtails.
* RoseHairedSweetie: She's definitely the cutie and probably the least militaristic of the protagonists, fitting her pink hair.
* SignedUpForTheDental: Joined the military as a way to exercise and lose weight.
* SuspiciouslySimilarSubstitute : To Eri
* StunGuns: She uses a taser as her melee attack.

[[WMG: Trevor Spacey]]

Trevor received his first computer at age three. By the time he was seven, not only could he perform complex coding, he also worked on creating antivirus progams during summer break, many of which are still in use at the school he attended. When he ended up joining the Peregrine Falcons, he found a great deal of respect for Marco, whose own computer skills surpassed his own. Here, he acted as Tarma's stand-in. His melee involves kicking the enemy so hard, it shreds them apart; he gains double points for this, but he has to hold still.

!!Trevor Spacey Tropes:

* ArmedLegs: His melee is a powerful kick called Knife Boots.
* AsianAndNerdy: Korean and a PlayfulHacker.
* {{Bishonen}}: Compared to the other male characters, he's young and boyishly handsome.
* PlayfulHacker: A point which causes him to get along with Marco, another playful hacker.
* TheSmartGuy: An ingenious hacker.
* SuspiciouslySimilarSubstitute : To Tarma, who was not playable in his game.
* WeaponOfChoice: The Two Machine Guns.
!!Metal Slug Advance

[[WMG: Walter Ryan]]

Walter joined the Peregrine Falcons squad with the hopes to train his mind and body, knowing he had the stamina to keep up with the rest of them. However, he never would've guessed his initial "training" would turn out to be a rescue mission.

* FallingIntoTheCockpit: An early training mission became a very real mission as his drill instructor turned out to be TheMole.
* MamasBoy: His hobby is listed as "phoning his mama."
* PaletteSwap: To Marco.
* SuspiciouslySimilarSubstitute: Again, to Marco as the main "guy" character.
* YouGottaHaveBlueHair: His hair is literally blue. No mention is made of this.

[[WMG: Tyra Elson]]

Tyra's strong desire to fight evil is what motivated her to join the Peregrine Falcons alongside Walter. After getting the highest score on the written test, she was immediately put to the physical training course on the island where the game takes place.
* BareYourMidriff: Not normal combat attire, even for a trainee.
* FallingIntoTheCockpit: An early training mission became a very real mission as her drill instructor turned out to be TheMole.
* PaletteSwap: SHe uses an edited version of Nadia's sprites.
* RevolversAreJustBetter: Defaults to a revolver, as shown in her official art.
* TheSmurfettePrinciple: The only female to be a member of the PF Squad. Every other female is on the SPARROW Squadron.
* SuspiciouslySimilarSubstitute: Has the same outfit as Nadia, her hair is also a red hue, and introduced as a new female character along side a new male character.
!Crossover Appearances

Ralf and Clark, the IkariWarriors, in between their appearances in ''VideoGame/TheKingOfFighters'' series, appeared alongside the core team for Metal Slug 6, and are back for Metal Slug 7/XX. Joining them in XX is Leona. A better amount of information about these three can be found on their respective series' page.

[[WMG: Ralf Jones]]

Aside from his participation in various fighting tournaments, little to nothing else is known about him or Clark. There's rumors flying around, but he tends to ignore them.

Though carrying half as much ammo and grenades as anyone else, Ralf makes up for this with his Vulcan Punch, capable of destroying tanks, and his melee speed is much faster than anyone else's (and his normal melee can also damage things that others cannot). He's also the only character capable of taking two hits. He's just that tough.

* {{Badass}}: Can take nukes to the face and live and destroy tanks by punching them.
* DashAttack: His ''other'' special move, the Galactic Phantom Punch.
* HeterosexualLifePartners: With Clark.
* HotBlooded: The guy is willing to charge a tank with his bare hands.
* KnifeNut: Collects knives as a hobby. Though ironically he's one of the few that doesn't use them on the battlefield.
* LightningBruiser: He can run and jump as well as everyone else, has fast (and highly damaging) melee attacks, and takes 2 hits to kill, unlike most of his allies.
* MadeOfIron: Why can he take a tank shell? Just because he's that damn tough.
* RedOniBlueOni: The red to Clark's blue.
* OneHitPointWonder: Averted; he can take ''two'' hits.
* WeaponOfChoice: The Flame Shot.

[[WMG: Clark Still]]

Clark and Ralf have been longtime friends, even in the unit the two of them are assigned to.

Clark's unique ability is his Super Argentine Backbreaker, a special melee move capable of earning him a lot of points in a short time frame. He also gains a small window of invulnerability with each enemy he tosses with this. However, it only works on certain human-sized enemies.

* CoolShades: Much like Tarma. Echoing Tarma's relationship with Marco, the shades serve to differentiate Clark and Ralf.
* DifficultButAwesome: If you can overcome its short range, the Super Argentine Backbraker will rip nearly any hoarde of (human) mooks a new one.
* HammerSpace: In ''Defense'', his special move is to pull out a large ExplodingBarrel and hurl it.
* HeterosexualLifePartners: With Ralf. They've been together for years in several combat theaters.
* RedOniBlueOni: The blue to Ralf's red. He's less hot blooded and more stoic.
* TheStoic: Even when suplexing enemy soldiers, he's not exactly a ScreamingWarrior.
* WrestlerInAllOfUs: His Backbreaker.
* WeaponOfChoice: The Iron Lizard.

[[WMG: Leona Heidern]]

Leona was adopted by Commander Heidern following her involuntary transformation and slaughter of her hometown, and Clark and Ralf helped to oversee her training.

Leona joins the team for XX, but has to be unlocked via DLC (she's only 99 cents, well worth it). She carries an amalgamation of everyone else's skills (Stronger pistol fire, 20% more ammo and grenades, Slugs can take an extra hit, and she retains her weapons after losing a life. Interestingly, her special melee, Moon Slasher, can destroy bullets). According to her profile, Clark, Fio and Leona finished a mission that also further bonded the three as being good friends.

!!Leona Heidern's tropes:

* AllYourPowersCombined: In ''XX'', she has basically everyone else's special skills.
* AscendedExtra: Originally appeared in a cheap cell phone game before being moved to the main series.
* CloseRangeCombatant: In ''Defense'', her moon slasher is her only move.
* GuestFighter: She originates from the ''VideoGame/KingOfFighters'' series.
* SignatureMove: Her Moon Slasher
* TrueCompanions: With Ralf and Clark, ever since ''KOF '96.''
!Antagonists (By game appearance)

!!Metal Slug

[[WMG: Donald Morden]]

Morden was formerly a Vice Admiral in the Regular Army Marine Corps. Though a tough and efficient commander, he was also something of AFatherToHisMen, which greatly earned him their respect.

Things went well for Morden, up until the Central Park bombing, which not only took away his right eye (hence the eyepatch he wears), but it also killed his young son. To twist the knife even further, he later found out that Regular Army Intelligence knew about the bomb threat and pushed for the high command to stop it, but due to rampant corruption in the system at the time, the higher-ups dismissed the threat as being a mere prank or so (later blaming the bombing on a lack of intel), which, when combined with his emotional instability and rampant alcoholism following afterwards, ended in Morden's resignation.

When Morden left, all of the soldiers under his command (including Allen O'Neal) followed him out of sheer loyalty to him. This allowed him to form the Rebellion Army, and he began making swift tactical moves against the Regular Army, nearly destroying them and finally motivating them to get their act together. In fact, during his attack on the president, he gained his nickname as the "Devil Rebirth", due to just how frightening he was.

Though he was a main threat in Metal Slug, in Metal Slug 2 it turns out he teamed up with the Mars People, who gave him the technology he needed, but were quick to turn on him. He barely showed up in games 3 (where a Mars Person was impersonating him) and 4 (there were robotic duplicates of him, possibly including the one in the intro demo), and was completely absent in 5, but made a return in 6, where he, again, made a pact with the Mars People, but this time, due to the Venusians invading, it was soon under different terms. Taking a certain route in Stage 4 will mean that he's the one who actually saves the player at the end of the game.

His biggest return to the spotlight was in 7/XX, where it turns out his own soldiers, from some unspecified time in the future, went back in time to help him out, again out of sheer loyalty to him.

!!Morden's Tropes

* BigBad: For most games, though sometimes he gets the title hijacked.
* ButtMonkey: Appearing on screen is usually a sign that he'll suffer a HumiliationConga.
* EvilLaugh: Tends to laugh in a mocking tone upon approaching the player.
* EyepatchOfPower: The man certainly looks imposing thanks to his eyepatch.
* FinalBoss: Of the original and of ''7/XX''.
* IneffectualSympatheticVillain: He routinely gets defeated by the heroes, betrayed and outwitted by other villains, and all around humiliated. The only game where he wasn't overshadowed by another villain was 7/XX and he was only a major threat there because soldiers from the future came back in time to assist him with better technology.
* JokerImmunity: Despite being defeated and/or double crossed whenever he appears, he always survives to lead his army again.
* MadeOfIron: When riding in the Hi-Do in the first game, he can take [[UpToEleven even more bullets]] than [[SugarWiki/MostTriumphantExample Allen O'Neal]].
* MadeOfPlasticine: Applies to his troops
* NotMeThisTime: Against all expectations, he is ''not'' the main villain of ''4.'' The Amadeus syndicate actually abuses this expectation, having robot copies of both Morden and Allen.
* WellIntentionedExtremist: Distraught over the death of his son in a terrorist attack that could have been prevented and angered at corruption in the Regular Army, he abandoned the Regular Army and formed his own terrorist group, the Rebel Army, and while he plans on removing corruption from the world, his ultimate goal is to create a world wide military dictatorship.

[[WMG: Allen O'Neal]]

Morden's right hand man and bodyguard. When Morden resigned from the Regular Army, Allen, alongside all of Morden's supporters, followed him out. He's most remembered for taking insane amounts of punishment and supposedly being killed each game (he's eaten by an Orca in Metal Slug 2), only to return later. In Metal Slug 3, he not only died, but came back in the same level. Aside from being nigh unkillable, he also has a wife and son to return home to at the end of the day.

He appeared in Metal Slug 4's second and final stages, whereupon fighting him at the latter reveals him to be a machine, possibly meaning you also fought a robot Allen back in Stage 2. He comes back for Metal Slug 7/XX in a Rebel Gigant, still spouting his trademark quips and insults.

!!Allen O'Neal tropes:
* ADayInTheLimeLight : He's the player character for the (Japan Only) ''Metal Slug: Allen's Battle Chronicles'' game and its enhanced American port, ''Metal Slug Mobile 3''.
* AnnoyingLaugh: When he's not taunting the player, he usually can be heard going "AHAHAHAHAHA! AHAHAHAHAHA!"
* {{BFG}}: Wields a large machine gun whenever he's fought.
* BossBanter:
** "C'MON, BOY!"
* TheDragon: To Morden. Also doubles as TheBrute.
* {{Engrish}}: "GO HOME TO MOMMY!"
* JokerImmunity: Like Morden, he always keeps coming back, despite having been riddled with bullets and falling to his death in the first game, the second having him fall down to the ice water but apparently getting eaten by a giant Orca. The third game doesn't have anything notable besides him collapsing and falling about twenty feet, but his body still vanishes like regular enemies do after the fight.
* ImplacableMan: He cannot be stopped. Just shooting him alone is barely going to phase him.
* ImprobableWeaponUser: Get too close to him and he'll slap you with the ammo belt of his machine gun.
* LargeHam: He's the only character in the Metal Slug franchise to actually have spoken lines. And they are ''ALL'' taunts !
* MadeOfIron: He's a human (except in 4), just like the player characters. Unlike [[OneHitPointWonder the player characters]], he has an ''obscene'' amount of health for a human, being able to last longer than a tank!
* SeeYouInHell: His death cry.
* TurnsRed: His skin turns red as he takes more damage and speeds up.
* UnexplainedRecovery: All the time. Bonus points for Metal Slug 3 having him return during the attack on the Mars Peoples' Mothership despite you apparently killing him in the same level.
!!Metal Slug 2

[[WMG: Mars People]]

Aliens from Mars, if that wasn't obvious enough (though they do resemble squids, according to some). Possessing spaceships straight out of a 50's B-movie, they allied themselves with Morden, but were really using him to weaken Earth's defenses so they could take over with little to no opposition. Though defeated at the end of 2/X, they kidnapped Morden before the events of 3, sending a Mars Person to impersonate him, and eventually capturing one of the player's characters and creating clones of him/her.

At the onset of Metal Slug 6, it appears as though they've allied with Morden again, but this time it was to find their leader, Rootmars. Unfortunately, the Venusians showed up before Rootmars could be fully extracted, and they spent the rest of the game imprisoned at the Venusians' lair, if they weren't outright killed or eaten.

Taking a certain route in Stage 5 of 7/XX will show that the Mars People are back, and at the end of the game, just as Morden's about to be taken into custody, the Mars People swoop down and take him to safety.

!! Mars People Tropes:
* AliensAreBastards: They just want to conquer and destroy without much backstory.
* AlienBlood: They bleed green.
* ChronicBackstabbingDisorder: They betray Morden twice, for no reason other than because they can.
* EverythingsSquishierWithCephalopods: Resemble giant squid or octopi.
* {{Expy}}: They look exactly like H. G. Wells' martians.
* GiantSpaceFleaFromNowhere: In Metal Slug 2. Not so much in X, where they are foreshadowed better.
* HoistByHisOwnPetard: Both their betrayals of Morden and the Rebel Army lead to an EnemyMine that causes their defeat. The first time because a pilot from the Rebel Armor [[RammingAlwaysWorks rams their mothership]] and forces it to retreat, the second because the Rebel Army provides the player character with a rocket that allows them to reach their mothership.
* LastEpisodeNewCharacter: They show up in the last level of ''2''.
* RayGun: They wield these, just like classic aliens... although said guns tend to fire out slow, homing, destructible nucleus-like projectiles.
* StarfishAliens: They resemble giant jellyfish/squid. Yet they have skulls, green blood, and mouths.
!!Metal Slug 3

[[WMG: Rootmars]]

The leader of the Mars People, he was the one who orchestrated the events of 2/X and 3. Though originally looking like a larger Mars Person (just wearing a see-through helmet), his real form was revealed after his spaceship was destroyed (and he looked an awful lot like E.T.) He was defeated at the end of 3, his brain being blown out, and sank into the ocean, presumedly dead...

..But he wasn't. At the beginning of Metal Slug 6, Morden and the Mars People were looking for his body, and just as they located it, the Venusians came in. It turns out that while he was on the ocean floor, Rootmars had apparently recovered from his freefall beating at the hands of the team, and learned his lesson as well. During Stage 4, if you take the alternate route, Rootmars will swoop down and grab your player, taking him or her to the next destination whilst also being outfitted with two gatling guns, helping take down the Venusians. Taking this route also means Rootmars saves you at the end of the game.

!! Rootmars' tropes:
* BigBad: Of ''3''.

* EldritchAbomination
* FinalBoss: Of ''3''.
* FreeFallFight: You fight him while you and the soldier you rescued (and another player, if any) fall down to Earth.
* GoodScarsEvilScars; He has a number of Frankenstein-like stitchings on him.
* GreaterScopeVillain: He's the one who masterminded the alien invasion in ''2/X'' but was not seen in the game. You do fight his mothership, however.
* LargeAndInCharge: The normal Mars People are human-sized, he takes up most of the screen you fight him on.
* MyBrainIsBig: Bonus points for it actually being visible, encased in a dome.
* PsychicPowers: Fitting for an alien with a giant brain, it has psychic powers.
* SuperIntelligence: Part of the reason he's the leader of the Mars People.
!!Metal Slug 4

[[WMG: Amadeus Syndicate]]

A mysterious organization whose threat to the world was the release of the "White Baby Virus", a supervirus powerful enough to penetrate any mainframe's defenses. It also appeared as though Morden was supporting their efforts, though they had made a robotics plant at their base, creating several Morden bots, possibly including the one seen in the opening sequence.

The main man himself supposedly died at the end of the game when his base was destroyed, making him the first antagonist in the series to die for good. However, the credits sequence showed an intact computer broadcasting something.....

* EvilOldFolks: Amadeus himself
* FramingTheGuiltyParty: Their soldiers dress up as Morden's troops, and they have robot Mordens and Allens, presumably to invoke this trope.
* TheCracker: The Amadeus Syndicate are a team of cyber-terrorists.
* MechaMooks: Employ a lot of these.
!!Metal Slug 5

[[WMG: Ptolmaic Army]]

This army group attacked a Regular Army base and ended up stealing a disc containing blueprint data on both Metal Slugs and Rebellion Tech, which lead to them creating their own bastardized and upgraded versions. Due to the confusing nature of the game (and the fact that so much went unused), it was hard to tell who was really in charge. It appeared as though they had gained the trust of the natives by the Corridor of Fire, and was using them to keep intruders away.

* {{Expy}}: Of the Rebel Army. Most of the enemies are even edits of Rebel soldier sprites. They're also one to the [[Franchise/CommandAndConquer Brotherhood of Nod]].
* KnightOfCerebus: While Metal Slug 5 has most of the series usual silliness, the Ptolmaic Army's typical soldiers lack the silliness of the Rebel Army
* PowerCopying: They specialize in stealing technical plans from the Regular and Rebel Army
* ReligionOfEvil: They are led by Ptolmaic Shamans, and apparently worship Scyther

[[WMG: Scyther]]

The FanNickname given to the FinalBoss of Metal Slug 5, a huge GrimReaper like demon that, we have no idea who this thing is. It just shows up at the end of the last stage and serves as the FinalBoss.

* AttackOfTheFiftyFootWhatever: Aside from the Mars Peoples' mothership (which is big enough to serve as an entire stage), it's easily the largest boss in the series, which is no small feat by any means.
* AutobotsRockOut: The battle against the Scyther has a heavy metal remix of the "Final Attack" theme.
* BackgroundBoss: Spends most of the fight in the background, and you have to [[AttackItsWeakPoint shoot the glowing skull on its chest.]]
* BigBad: Is presumably this for ''5'', [[GiantSpaceFleaFromNowhere but we may never know.]]
* DramaticThunder: Thunder and lightning strikes when the boss makes its appearance.
* EldritchAbomination: A gigantic demonic creature that [[CelestialBody looks like it was made from the fabric of space itself]]. It also has a skull in it's chest that serves as it's weak point.
%%* FinalBoss
* GiantSpaceFleaFromNowhere: Seriously? Where the hell did this thing come from? There's no explanation it was allied with the Ptolmiac Army, or if it was their leader, or if they were a ReligionOfEvil and its their GodOfEvil they were summoning to bring about TheEndOfTheWorldAsWeKnowIt.
* KnightOfCerebus: Whatever this thing is, it's design is very much DarkerAndEdgier compared the usual bosses that appear in the series and is actually very menacing.
* PlayingWithFire: Most of its attacks will burn you to death should they kill you.
* ScrewThisImOuttaHere: It doesn't die when defeated, it just flies away into the background.
* SinisterScythe: Which appears to be forged out of flames.

!!Metal Slug 6

[[WMG: Venusians]]

Obviously, aliens from Venus. The Mars People's nemesis, they not only appear to be physically stronger and more diverse than the Mars People, they also seemed to have better technology on their side as well. They formed the second half of Metal Slug 6's plot, especially after their first appearance was snatching up two martians and eating them.

Their queen came to Earth via an asteroid, and was quick to set up an underground shelter for her brood. After one hell of a fight against the team, she fell to her death, releasing an explosion that apparently killed the protagonists as well. Depending on which route you took in Stage 4, either Morden or Rootmars will save the player.

!!Venusians Tropes:

* AliensAreBastards: Even moreso than the Mars People.
* EvilIsVisceral: They have an organic lair as opposed to the Mars Peoples' technological one.
* FoodChainOfEvil: Think the Mars People were deadly? These guys literally ''eat Mars People for breakfast''.
* GiantEnemyCrab: The Crab-tanks and Vanguards.
* KnightOfCerebus: The Mars People have an OhCrap reaction when they show up and eat them at the end of Mission 2. The final mission also has a DarkReprise of the classic "Final Attack" theme.
* HeliCritter: The Smashers, which spin their legs to fly in the air like a helicopter before inflating themselves to crash down on you.
%%* HordeOfAlienLocusts
* UniqueEnemy: There's a Gold Hunter Walker encountered if you take a secret path in the final mission, killing it grants 50000 points.
* SpinAttack: The lowest ranking mooks move around via spindashing.
%%* ZergRush

[[WMG: Venusian Queen]]
A huge alien that serves as the final boss of 6, and the leader of the Venusians.

* BackgroundBoss: Most of the boss is in the background- you need to attack her head to damage her.
* BigBad: The leader of the Venusians in ''6''.
* DisneyVillainDeath: Falls to her death before explodes in a massive explosion.
* EyeBeams: Purple ones that aim at you.
* FinalBoss: Of ''6''.
* FlechetteStorm: Has an attack where she charges energy then releases it in crescent projectiles. Then they fly at the player from the left and right, or may even converge on them from all directions.
* HoldTheLine: The final part of the battle turns into a FreeFallFight where she's invulnerable, sending ''huge waves'' of destructible projectiles dowanwards at you.
* LargeAndInCharge: She's one of the biggest Venusians there.
* TrickBoss: You face off the pod she's encased in. It stays there, doesn't do anything, and is periodically accompanied by Venusians. When beaten, a bunch of Morden soldiers come in to celebrate with a victory music of sorts... and then her eyes light up and destroy the soldiers. Time for the ''real'' boss.
!!Metal Slug 7/ XX

[[WMG: Future Soldiers]]

Morden's own troops from an unspecified time in the future. Presumedly at some time after Morden was captured or killed, his own forces, again out of loyalty, gathered up their technology and, though the construction of what appeared to be a time window or portal, went back in time to help Morden out. Despite having new weapons and upgraded machinery, they still got their asses handed to them, and with their window destroyed, they were unable to do anything else.

!!Metal Slug Advance

[[WMG: Allen Junior]]

That's right, Allen's own son is here. He posed as a training instructor, which allowed him access to the island where the Peregrine Falcon trainees were undergoing the test. From here, he was able to lead some of Morden's forces to launch a surprise attack on the trainees, capturing the most of them and allowing Morden's troops to set up a base.

Unlike his father, though, Junior tends to act more strategically in direct confrontation against the player. However, once injured past a certain point, he eventually loses his temper and starts acting more like his father in battle. However, finding and defeating him is easier said than done.
!!Metal Slug 3D

[[WMG: Oguma]]

Pronounced Ogma, he is the head of the ridiculously massive company named after himself, Oguma was apparently funding Morden's efforts, but was actually using him to help find a recording device deep underground, the Alator. It turns out that Oguma was one of few survivors of a long-extinct race, the Tuaha de Dunan, who were shown to be technically advanced.

His culture was said to self-destruct at the peak of their evolution; to combat this, they placed a recording device on a planet, then hibernated for 300 million years. If the information gathered by the device clashes with them, they simply erase the world's history and start over, which has possibly caused some time-space problems.

Near the end of the game, after betraying Morden, he used the Alator to release the Lugas, which then absorbs the information from Alator and begins its mission to erase history, prompting the crew to stop it. When Lugas was absorbed by a previous experiment, the Luu (and beaten by the crew afterwards), it goes crazy as Oguma and his followers stay behind in an attempt to further stop it, despite Marco's protests.

At the game's end, as Rumi is about to head out, Oguma shows up out of nowhere and hands her his information disc before leaving, hoping the people would learn from his prior mistakes.

!! Oguma Tropes:
* AffablyEvil: Speaks in a very polite and calm voice.
%%* AntiVillain
%%* KnightTemplar
* TheStarscream: Betrays Morden halfway through the game after showing his true colors, and eventually becomes the game's BigBad.
%%* SufficientlyAdvancedAlien
%%* WellIntentionedExtremist
!Support Characters and other notable NPC's

[[WMG: Rumi Aikawa]]

Rumi originally joined the Regular Army to make use of their medicinal facilities to help her ailing mother, who had a weak heart, and her twin sister Madoka, who was physically ill. Due to a paperwork SNAFU, she was shipped to the front lines, and despite having never completed her training, she made it back unscathed, a miracle in and of itself.

She was offered the chance to leave and live life as a civilian, but she declined the offer, and was soon transferred to the Supply Division. Before each mission, she fills her backpack with various supplies, and treks out to deliver the goods to Regular Army Soldiers... but there's one problem. She's horrible with directions, and is likely to wander off and be found in a completely different location, earning her the nickname "The Wandering Ghost" by most soldiers. She later found out her sister Madoka also joined to become more physically fit, and was also placed in the Supply Division..... and shares the same atrocious sense of direction her sister has.

Though mostly a background character in the main games, she was given a bigger role in Metal Slug 3D, giving information to Marco and even allowing access to a Garage where the player could customize their own Metal Slug vehicle.

[[WMG: Hyakutaro Ichimonji]]

A Second Lieutenant of the Regular Army, he's a living legend among the soldiers. Pretending to be a captured POW, once he's "rescued" by the player, he helps out by firing homing Hadokens at the enemies and spin-kicking anyone else who gets too close. He will flee if you die, though.

!!Hyakutaro Ichimonji tropes:

* KamehameHadouken: His main attack has him fire a ''homing'' hadouken at enemies. It also deals pretty good damage too.
%%* KiAttacks
* ObfuscatingStupidity: He pretends to be a captured POW. Once he's "rescued", however... It's noted that he does this ''on purpose''.

[[WMG: Utan]]

An Israeli orangutan that wears a diaper and carries an Uzi.

!! Utan Tropes:

* BadassNormal: Compared to the main characters.
* EverythingsBetterWithMonkeys
* GagPenis: If you look at his IdleAnimation close enough, you'll notice he pulls out 3 bananas out of his diaper and eats them, after which he tries it again but pulls out his [[IncrediblyLamePun monkey dong]] instead, blushes and quickly stuffs it back inside.
* StockAnimalDiet: As a monkey, he eats bananas.

! Combat School Instructors

[[WMG: Sophia Greenville]]

The drill instructor from Metal Slug 1 (Neo Geo CD and PSX).

!! Sophia Tropes:

* BabiesEverAfter: Margaret, the instructor from Metal Slug X hints that Sophia retires to raise a family.
* MsFanservice: There's a good amount of art dedicated to her in the art galleries of the home versions.
* PassionateSportsGirl: What made her easily excel as a member of the Peregrine Falcons. Her favorite sport is Basketball, and also dabbles in bass fishing.

[[WMG: Margaret Southwood:]]

The drill instructor of Metal Slug X.

!! Margaret Tropes:
* EyesAlwaysShut: [[OOCIsSeriousBusiness If she opens them]], you've either impressed her, or you've made a complete ass of yourself.

!The Slugs

[[WMG: SV-001]]
The first Slug in the series, and the titular Metal Slug. Capable of shooting a vulcan machinegun 360 degrees and a low-velocity round forwards but incapable of turning around, and has a reduced jump. Variations include the Type-R, which sacrifices power for maneuverability, the Experimental, which sacrifices maneuverability for power, the Type-B, which is stronger in all areas, the Bronze, which is never used by the player, and the Black Hound, a Ptolmaic-made variation the is remotely controlled and equipped iwth a laser and homing missiles.

!!SV-001 Tropes
* ArmorPiercingAttack: Any of them can acquire Armor Piercing Shells, which do extra damage against enemy tanks, and, most importantly, fly all the was across the screen and are spammable.
* AllYourPowersCombined: The Type-B has the positive traits of the Experimental and the Type-R
* BackwardsFiringGun: The SV-001 Type-R in the first level of the third game has the unique property of firing in the direction opposite the player points. This is important, since the first boss is spent frantically running away from it.
* EscapePod: They are equipped with a floatation device, which is buoyant enough that the player can survive falling from ''space'' with it.
* MiniBoss: The Black Hound first appears as an optional boss in ''5'' before becoming playable in ''Advance.''
* MightyGlacier: They all take two to five hits to the player's one. However, their overall slower speed and lower jump height also makes dodging harder.
* RedOnesGoFaster: The Type-R is orange.
* SuicideAttack: Pressing Fire and Jump while in it will cause it to rush forward and explode.

[[WMG: Slugnoid]]
A sideways-walking, high-jumping slug designed for mountainous terrain. First appears in ''2'' and has had consistent appearances since. It is equipped with two Vulcan Cannons, as well as a third, downward facing cannon, whose ammo varies depending on the game. The standard Slugnoid and the higher-grade blue-tinted Type-B use Flame ammo, which spreads in all directions when hitting a surface, while the Walker Slugnoid and the deep-red Slugnoid Type-R fire Fat Lizards. The Type-B features even greater jump height.

!! Slugnoid tropes
* ActionBomb: The Fat Lizard ammo, used by the Walker Slugnoid and the Type-R, which is a small ball with legs that runs to the left of the player, then explodes.
* [[ThisLooksLikeAJobForAquaman This Looks like a Job for Slugnoid]]: It's only ever really able to shine in situations that require more vertical movement than horizontal. In ''2,'', the fact that its missile travel ''downward'' means its only really useufel when an enemy is directly below you. It appears to be designed with fighting the second boss of ''2'', its first appearance, in mind.
* GlassCannon: While its firepower is stronger than the Slugnoid, it's very cumbersome to use, making it hard to keep it around. In comparison to other Slugs and the players it's still a mighty glaciar.
* InASingleBOund: The Slugnoid's specialty, which is improved even more for the Slugnoid Type-B.
* JumpJetpack: Its high jumps are jetpack-assisted
* MoreDakka: It has ''two'' cannons as opposed to one.
* RedOnesGoFaster: The Type-R, but it's still not as fast as even the SV-001 Experimental.
* ShowsDamage: Taking damage causes the Slugnoid to lose a gun.
* WalkingTank: It's on two short, if stubby, legs.

[[WMG: SV-Camel]]
A camel equipped with one or two Vulcan Cannons. First appearing in ''2'' to assist the player during the first Arabian levels, it leaves the player during the second. After returning when the protagonists return to the desert in ''3'', it remained absent from the series until ''Defense.'' It is notable for being the first animal Slug in the series. it does not carry its own bombs, so the player instead throws their own grenades while on the camel.

!! SV-Camel tropes
* [[AutomatonHorse Automaton Camel]]: Averted in one instance. After the first level of ''2'' or ''X'', it will neglect to follow the protagonist, to remain near a water source. Otherwise, it is incapable of being hurt.
* DenialOfDiagonalAttack: While its cannon can fire in all directions, it can't turn around. So you will only be able to throw grenades forward while on it.
* FragileSpeedster: Faster than the other tanks, and faster than the player when runnning. However, outside of elevating the player above low-ground attacks, it offers no protection.
* LovableCoward: It refuses to follow the protagonists into an ancient tomb, or into an army of man-eating plants, but is invincible when you do have it.
* NonIndicativeName: It's actually a Dromedary, not a camel.
* TruthInTelevision: Camel-mounted machine guns actually existed in real life, called ''zamburaks''.

[[WMG: Slug Flyer]]
A tiny jet first appearing in ''2'', and every game except ''4'' since. It's equipped with two 10mm cannons which can fire 30 degrees above or below it. It's only variation is the Slug Jet, which is controlled by an NPC instead.

!! Slug Flyer tropes

* HomingProjectile: It's missiles orient themselves slightly on their own.
* JetPack: Starting in ''3'', many of them contain a jetpack and goggles for the player, for if the Flyer gets destroyed.
* ThisLooksLikeAJobForAquaman: Only ever available when enemy planes are about.

[[WMG: Elephant Slug]]
A weaponized elephant found in a Sasquatch cave in ''3.'' After freeing it from a tomb of ice, the player can ride to gain an advantage against invading zombies, who have slaughtered the native Sasquatches. It is capable of shooting electricity and fire from its trunk.

!! Elephant Slug tropes
* FireBreathingDiner: To gain the ability to shoot fireballs, it must pick up a hot pepper.
* MightyGlacier: While it does not technically offer any protection, it is so tall that almost no zombies that are on the same floor as the player can hit them. Meanwhile, it can't jump is as slow as molasses.
* ShaggyDogStory: It starts to help you after you free it from the ice its trapped in. In the end, the player either abandons it among the zombies or leaves it trapped in another pool of ice.
* ShockAndAwe: It can breathe electricity if it ears a car battery.
* TrampledUnderfoot: It can kill a zombie merely by walking over it.

[[WMG: Slug Mariner]]
A small one-seater sub with a high mass Vulcan and torpedoes that sink to the floor, which appears in ''3'' and ''5''. A variation, the Slug Sub, is capable of anti-air combat and has an additional supply of depth charges.

!! Slug Mariner tropes

* CaveBehindTheFalls: One inexplicably holds two Mariners in the third stage of ''3''.
* InertiaIsACruelMistress: It uses high-mass rounds, giving it serious difficulty when shooting from below
* SuperPrototype: The Slug Sub is actually the ''prototype'' of the Slug Mariner, despite its more diverse moveset.