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.

Characters who debuted in ''Metal Slug Defense'' and ''Metal Slug Attack'' can be seen [[Characters/MetalSlugDefense here]].

!Protagonists (Broken down by game appearance)

!!''Metal Slug''

[[folder: 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.
* 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.
* OverprotectiveDad: Put a programming lock on ALICE to keep certain ďadultĒ terms, particularly those dealing with charm and seduction, from even entering her vocabulary.
* PlayfulHacker : During his spare time. He accidentally almost launched nuclear weapons at one point.
* TheSmartGuy: Outside the battlefield he's an expert hacker.
* TrulySingleParent: He's the "father" of [=MS-ALICE=].
* VitriolicBestBuds : With Tarma
* WeaponOfChoice: The Heavy Machine Gun, but initially it was the standard Pistol.

[[folder: 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.
* DemotedToExtra: Becomes a supporting character in ''4'', but regains his playable status in ''5''.
* 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''

[[folder: 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.
* BareYourMidriff: Setting a trend, her military "uniform" exposes her belly.
* BrutalHonesty: In her first mission with Fio, Eri was blunt saying that her inexperience in combat was going to get them both killed, and that Fio was better hanging back so Eri could go on alone.
* TheBigGirl: While the whole team packs plenty of power, she's the explosives specialist.
* CompressedHair: Hidden in her bandana in her sprites. Some pieces of official art would have some of her hair spew out of her back head.
* 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''.
* DemotedToExtra: Becomes a supporting character in ''4'', but regains her playable status in ''5''.
* 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. Made more apparent in ''Attack,'' where one of her strongest memories is abandoning Fio on her first few missions because she was too slow.
* InSeriesNickname: "Memphis Bomb Princess".
* JapaneseDelinquents: A variation. Eri was a former ''sukeban'' (female gang leader) and she still sports blond hair.
* {{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). It is unknown if her blond hair was a leftover of her childhood as a ''sukeban''.
* SdrawkcabName: Spelling her name backwards in Hiragana will get the name of a famous Japanese pop star Rie Tomosaka.
* 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.
* YoungerThanTheyLook: Eri's two years younger than Fio, considering Eri's tougher personality.

[[folder: 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.
* FingerPokeOfDoom: Her melee attacks include [[DualTonfas swift tonfa strikes]], [[AnAxetoGrind hatchet slices]], and [[WimpFight sissified slapping and shoving]]. Enemy soldiers die horribly all the same.
* GirlyBruiser
* GuestFighter: She is playable in ''VideoGame/TheKingOfFighters: Maximum Impact 2''.
* HeterosexualLifePartners: With Eri.
* HeroicSelfDeprecation: She usually thinks less of herself in comparison to her teammates.
* LastOfHerKind: Fio's parents' greatest fear. See StayInTheKitchen below.
* {{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.
* OlderThanTheyLook: Despite her appearance and character, Fio is two years older than Eri.
* SmallGirlBigGun: The heavy weapons specialist is the smallest of the four main playable characters.
* StayInTheKitchen: Fio'a father would rather she not be in combat so damn much. Whether it's because she's a woman or because she's an only child (LastOfHerKind and thus putting the whole family line in danger since she has no children of her own) is up for debate (possibly both).
* 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, but initially it was the Heavy Machine Gun.

!!''Metal Slug 4''

[[folder: 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: [[RuleOfSexy Not that it isn't a standard with the Regular Army in general]].
* BigEater: Compared to the other characters whose powerup relies in eating, she takes it UpToEleven. Her idle animation almost always leads her grabbing a bite on a chocolate bar.
* FormerlyFat: Well, except the ending has her eating a big feast alongside the other heroes.
* {{Gainaxing}}: Whenever she does her close-range attack in her Valentine's Day outfit.
* GirlyBruiser: Especially her Valentine's Day outfit in ''Defense'' and ''Attack''. [[LethalJokeCharacter This doesn't stop her from kicking ass, though.]]
* 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.
* MundaneUtility: Joining the military in the midst of conflict seemed like an easier way to lose weight than eating less.
* RoseHairedSweetie: She's definitely the cutie and probably the least militaristic of the protagonists, fitting her pink hair.
* SpyCatsuit: "Special Nadia's" outfit.
* SignedUpForTheDental: Joined the military as a way to exercise and lose weight.
* SignificantGreenEyedRedhead: RoseHairedSweetie with green eyes in her portrait.
* StunGuns: She uses a taser as her melee attack.
** SetSwordsToStun: Inverted. Her taser is set to essentially killing her victims outright like the rest of the team's melee attacks.
* SuspiciouslySimilarSubstitute : To Eri, in terms of animations.
* WeightWoe: The reason she joined the military is to lose weight, going up her needs to become a supermodel. Unfortunately this gets conflicted to the fact when she's admitted to be a known BigEater.

[[folder: 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.
* ChildProdigy: Literally owns and uses a computer since he was [[ImprobableAge three years old]].
* TheCracker: Zigzagged with PlayfulHacker. Becomes the Regular Army's support hacker and a sideline commando.
* NonstandardCharacterDesign: Sprites-wise, Trevor is the only male who normally has sclera around the pupil (most have BlackBeadEyes).
* ObliviousToLove: More like he doesn't know that [[CrushBlush Abigail blushes]] at the sight of him.
* 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''

[[folder: 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.
* WeaponOfChoice: The Drop Shot.

[[folder: 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.
* WeaponOfChoice: The Super Grenade Launcher.
!Ikari Warriors

Ralf and Clark, 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 and later Whip and Heidern in ''Metal Slug Defense''. A better amount of information about these five can be found on their respective series' page.

[[folder: 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.

* 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.
* OneHitPointWonder: Averted; he can take ''two'' hits.
* RapidFireFisticuffs: His special move, the Vulcan Punch.
* RedOniBlueOni: The red to Clark's blue.
* WeaponOfChoice: The Flame Shot.

[[folder: 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. In ''Attack'', his "Jet Clark" variant throws refrigerators.
* 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.
* StoneWall: As Jet Clark, his ability to throw refrigerators to use as blockades make him very hard to wear down.
* WrestlerInAllOfUs: His Backbreaker.
* WeaponOfChoice: The Iron Lizard.

[[folder: 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.
* CatGirl: By donning cat ears, she can decrease her hit points while increasing her attack.
* 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.''

Whip makes her debut in ''Metal Slug Defense'' as part of the ''King of Fighters'' faction. Since the ''KOF'' faction does not exist in ''Metal Slug Attack'', Whip has been moved to the P.F. faction.

!!Whip's tropes:
* CastHerd: Whip was separated from Ralf, Clark, and Leona in ''Defense'', since the latter three are part of the P.F. faction. While she eventually joined alongside them in the same faction in ''Attack'', Whip is not part of the Wrath team, rather being placed next to the Slugnoid Type-B for the Agent Sally team.
* LastEpisodeNewCharacter: Whip and Heidern were the final units implemented in ''Metal Slug Defense''.
* RevolversAreJustBetter: Her special attack is shooting a bullet from a golden revolver. Its range is short in ''Defense'' and much farther in ''Attack''.
* WhipItGood: Her standard attack. Her whip is able to cause knockback in ''Attack''.

[[folder: Heidern]]
Heidern makes his debut in ''Metal Slug Defense'' as part of the ''King of Fighters'' faction. Since the ''KOF'' faction does not exist in ''Metal Slug Attack'', Heidern has been moved to the P.F. faction.

!!Heidern's tropes
* CastHerd: Heidern was separated from Ralf, Clark, and Leona in ''Defense'', since the latter three are part of the P.F. faction. While he eventually joined alongside them in the same faction in ''Attack'', Heidern is not part of the Wrath team, rather being placed next to the Donkey Slug (Eri) for the "Operation Ikari" team.
* EarlyBirdCameo: Appeared as a drill instructor in ''Defense'''s Combat School before becoming a playable unit.
* HiredGuns: The leader of the Ikari Warriors, who sends his troops to the Regular Army whenever there's a big conflict.
* LastEpisodeNewCharacter: Whip and Heidern were the final units implemented in ''Metal Slug Defense''.
* LifeDrain: His special attack has him jump and suck the life of the closest unit.
* PrecisionFStrike: [[PunctuatedForEmphasis Go. To. HELL!]]
* RazorWind: His long-range attack.

!Antagonists (By faction)

!!Rebel Army

[[folder: Donald Morden]]
-->Debut: ''Metal Slug''

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.
* CoolPlane: Despite being an army general, he seems to have a strong preference to copters and planes over tanks. The few times he is in a tank, its a method of defense, not hiding.
* EvilLaugh: Tends to laugh in a mocking tone upon approaching the player.
* EvilerThanThou: Frequently on the receiving end of this.
* EyepatchOfPower: The man certainly looks imposing thanks to his eyepatch.
* FinalBoss: Of the original and of ''7/XX''.
* 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 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.
* TooDumbToLive: He allied with the Mars People a second time in ''3'' despite them betraying him in the last game. It goes as well as you'd expect.
* 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.

[[folder: Allen O'Neal]]
-->Debut: ''Metal Slug''

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 "YAHAHAHAHAHA! YAHAHAHAHAHA!"
* {{BFG}}: Wields a large machine gun whenever he's fought.
* BossBanter:
** "C'MON, BOY!"
* TheDragon: To Morden. Also doubles as TheBrute.
* DuelBoss: He almost always provides the player with a Heavy Machine Gun before his fight, to be a match against his own. in ''7'' he wield a Slug Gigant, which is matched by the player's own Gigant (though the fact that the two use the same weapon is happenstance in this case). The one time he uses a clearly advantagous weapon without giving the player something to compensate, [[spoiler:It turns out to be a duplicate.]]
* {{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. In ''Attack'' he gets impaled by Caroline's Augensterm and ''electrocuted'' in an Extra Ops story.
* LightningBruiser: Despite being bigger than the playable characters, he's also faster than them.
* 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.

[[folder: Abul Abbas]]
-->Debut: ''Metal Slug 2/X''

The leader of the Arabian forces, Abul Abbas made a joint alliance with the Rebel Army. After their defeat in mission 1, a few Arabian rebels show up in the beginning of mission 2 as a last ditch effort.

!!Abul's tropes:
* BadBoss: He has a terrible habit of refusing to own up to his own mistakes. In ''Attack'' he refuses to let his own troops stop to refuel their units, then blames them for running out of fuel at a critical moment.
* DummiedOut: Sprites of Abul attacking and setting up his white flag are present in ''2'''s [=ROM=]. These get their use in ''Defense'' and ''Attack''.
* HoistByHisOwnPetard:
** The player is able to kill Abul in ''X'' [[ if one of Iron Nokana's shots]] [[ lands on him]] during the [[ScoreScreen "Rescued Prisoners" screen]].
** Accusing his soldiers of laziness when they want to stop to refuel their vehicles bites him in the rear when their vehicles run out of fuel.
* IShallTauntYou: Shows up multiple times commanding his troops and taunting the player.
* KnowWhenToFoldThem: Waves a white flag once things go bad for him.
* StarterVillain: He serves as a first-level foe whose army is even worse equipped than the Rebels, and his troops lose all presence after the first level.
* TheUnfought: The player ends up fighting the mission's boss while ignoring Abul in the background.

[[folder: Future Soldiers]]
-->Debut: ''Metal Slug 7/XX''

Morden's own troops from an unspecified time in the future. Presumably 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.

[[folder: Allen Junior]]
-->Debut: ''Metal Slug Advance''

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.

!!Allen Junior's Tropes
* InTheBlood: He tries to act smarter than his father, and indeed becomes more successful in attacking the Regular Army than him, but in the end gives in to the same rage his father is known for.
* TheMole: He infiltrated the Regular Forces training camp by posing as a drill instructor.
* PistolWhipping: One difference from his father is that he does ''not'' typically use a knife, instead preferring to slam his opponent with his ammo belt, which is one of the few non-lethal attacks in the game.


[[folder: Mars People]]
-->Debut: ''Metal Slug 2/X''

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 Invaders showed up before Rootmars could be fully extracted, and they spent the rest of the game imprisoned at the Invaders' 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.
* FlyingSaucer: Their main vehicle. Their mothership is an even bigger one.
* 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''. Averted in ''X'' where they appear in earlier levels.
* 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.

[[folder: Rootmars]]
-->Debut: ''Metal Slug 3''

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 Invaders 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: He may look like E.T., but he does it Lovecraft-style.
* 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.

!!Ptolemaic Army

[[folder: Ptolemaic Army]]
-->Debut: ''Metal Slug 5''

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 Evil Spirit Incarnate.

[[folder: Evil Spirit Incarnate]]
-->Debut: ''Metal Slug 5''


The FinalBoss of Metal Slug 5, a huge GrimReaper like entity 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 Evil Spirit Incarnate 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.]]
* CelestialBody: Itís entire frame seems to be made out of the fabric of space.
* 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.
* EvilIsBigger: By far the biggest boss in the franchise.
* FinalBoss: With ''5'' allegedly being the last in chronology, the Evil Spirit Incarnate serves as this for the seriesí plot, as well as the last boss for ''5'' in general.
* FlamingSkulls: The skull in itís chest seems to be burning with an ethereal or cosmic substance.
* GenericDoomsdayVillain: Even by the standards of this series.
* GiantSpaceFleaFromNowhere: Seriously? Where the hell did this thing come from? There's no explanation if it was allied with the Ptolemaic Army, or if it was their leader, or if they were a ReligionOfEvil and its their GodOfEvil they were summoning to bring about TheEndOfTheWorldAsWeKnowIt.
* HellIsThatNoise: Produces a loud screech when it shows up next to the arena.
* KnightOfCerebus: Whatever this thing is, its design is very much DarkerAndEdgier compared the usual bosses that appear in the series and is actually very menacing.
* LeanAndMean: The silhouette shows that it is a very thin being.
* NonStandardCharacterDesign: Whereas everyone else is a human, an alien or a robot, we have a towering being thatís made of space.
* PlayingWithFire: Most of its attacks will burn you to death should they kill you.
* RedEyesTakeWarning: It has a piercing gaze with red eyes.
* ScrewThisImOuttaHere: It doesn't die when defeated, it just flies away into the background.
* SinisterScythe: Which appears to be forged out of flames.
* SinisterSilhouettes: Most of the time itís pitch black, only shown off by the thunder strikes.
* WingedHumanoid: Has large, bat-like wings.

[[folder: Ptolemaios]]
-->Debut: ''Metal Slug Attack''

Originally meant to be the FinalBoss of ''Metal Slug 5'', Ptolemaios makes his true debut in ''Metal Slug Attack'' as the main villain for the "Ptolemaic Attack" event. He is the leader of the Ptolemaic Army, controlling his troops within the shadows. He uses Sol De Rokker's red jewel to create a tower for himself that attacks with lightning and rosetta stones.

A side story revolves him annihilating the Red Goblin society, with Red Goblin seeking revenge.

!!Ptolemaios tropes:
* BadFuture: Ptolemaios is implied to be the winner in a future timeline. This results in two other characters going back in time where Ptolemaios has lower amounts of power.
* BigBad: Informally in ''5''. In ''Attack'', he is this to Red Goblin.
* TheCameo: Mostly unintentional, but his towers (as well as the Stone Turtle and the Elephants) can be seen in the background of Mission 5.
* CameBackStrong: Every death he suffers results in him getting new attacks.
* DeathFromAbove: Drops Rosetta stones on top of the opposing team.
* DummiedOut: A nearly complete set of sprites is present in ''Metal Slug 5''. Most of them are given use in ''Attack''.
%%* EvilOldFolks
* HijackingCthulhu: His Abyssal form's special attack is summoning the Evil Spirit Incarnate.
* ShadowDictator: How his description in ''Attack'' [[{{Handwave}} handwaves]] his lack of appearance in ''5''.
* ShockAndAwe: The bottom of his tower produces lightning strikes.
* TheUnfought: Was intended to have a boss fight near the end of the game, but it was DummiedOut.
* WhatHappenedToTheMouse: Due to ''5'''s rushed state.


[[folder: Invaders]]
-->Debut: ''Metal Slug 6''

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.

!!Invaders 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: The standard troops ambush in groups. In Mission 3, a large horde of them come spinning down from the right side.

[[folder: Invader Queen]]
-->Debut: ''Metal Slug 6''

A huge alien that serves as the final boss of 6, and the leader of the Invaders.

* BackgroundBoss: Most of the boss is in the background- you need to attack her head to damage her.
* BigBad: The leader of the Invaders 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 Invaders 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.

[[folder: Amadeus Syndicate]]
-->Debut: ''Metal Slug 4''

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.....

* TheCracker: The Amadeus Syndicate are a team of cyber-terrorists.
* EliteMooks: The disguised Amadeus troops use Heavy Machine Guns in the final level.
* EveryoneCallsHimBarkeep: Amadeus is referred to as "Doctor" in ''Metal Slug Attack''.
* EvilOldFolks: Amadeus himself
* FramingTheGuiltyParty: Their soldiers dress up as Morden's troops, and they have robot Mordens and Allens, presumably to invoke this trope. In the last level, they instead dress up as Regular Army troops.
* MechaMooks: Employ a lot of these.
* PaletteSwap: In ''Attack'', the Infantry are purple colored Rebel Soldiers.
* RobotMe: Robot Mordens and Allen O'Neils.
* SyntheticPlague: They managed to harness the Mummy and Zombie viruses from the previous games.
* VillainTeamUp: With the Rebel Army in ''Attack''. When Allen and Abigail were being ambushed by the robots, they assumed the Syndicate betrayed them. They were not; it was [[spoiler:the Syndicate's supervirus doing all the dirty work for her own.]]

[[folder: Oguma]]
-->Debut: ''Metal Slug 3D''

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:
* AbusivePrecursors: Oguma and his people essentially began life on Earth, but they have no problem snuffing it out in pursuit of their goals.
* AffablyEvil: Speaks in a very polite and calm voice.
%%* AntiVillain
%%* KnightTemplar
* ShoutOut: The Tuaha de Dunan are named for the pantheon of [[Myth/CelticMythology Celtic myth]].
* TheStarscream: Betrays Morden halfway through the game after showing his true colors, and eventually becomes the game's BigBad.
%%* SufficientlyAdvancedAlien
%%* WellIntentionedExtremist

[[folder: Pharaoh's Arc and the Mummy Army]]
-->Debut: ''Metal Slug Attack''

An expansion of the mummy enemies, the Pharaoh, Mummy Warrior, and Mummy Cat make their first appearance in the "Mummy's" event.

!!Tropes for all three characters:
* ActuallyFourMooks: Subverted. While the Pharaoh's Arc consists of multiple mummies on a chariot, they are all part of the same unit.
* DistractedByTheSexy: The Mummy Cats' main way of luring their enemies.
* DubNameChange: The Mummy Cats are called Sexy Mummies in Japan.
* EnemySummoner: The Mummy Cat's attack is to summon mummies that spit out poison bombs. If her third skill is unlocked, enemies hit by them have a chance to be stunned.
* KillItWithFire: The Mummy Warrior uses a long torch as his weapon.
* PaletteSwap: The Lovely Mummy is a red colored version of the Mummy Cat.
* SupportPartyMember: The Mummy Cat is awkward to use, but three of her four skills involve increasing the strength of Mummies, Mummy Warriors, and Mummy Dogs.
* VillainousBreakdown: The Pharaoh turns green in rage alongside his minions after being defeated. As the Tyrant Pharaoh, he starts commanding in a furious manner.

!Support Characters and other notable NPC's

[[folder: Rumi and Madoka 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 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, Rumi 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.

!!Rumi and Madoka tropes:

* ActionGirl:
** Promotional art for ''Metal Slug Defense'' shows Madoka parachuting while operating a bazooka. She is not a unit in ''Defense'' but she is in ''Attack'', using her bazooka from her backpack and throwing a medicine item to heal units.
** Rumi [[PromotedToPlayable turns into one]] in ''Metal Slug Attack''. She throws grenades from her backpack to her foes and tosses support items to her allies. Madoka gets added later, packing a Bazooka with great range and a humongous rate of fire and healing the front line.
* BewareTheNiceOnes: These two have some obscenely powerful Normal attacks in ''Attack''.
* ButtMonkey: A minor one, tagging either one of the sisters will cause them to fall to the floor and shooting them from the back tears their backpack open, dropping various items. The former also occurs when the player taps on Rumi on both tower defense games.
* CombatMedic: Madoka's special in ''Attack'' heals friendly troops.
* TheChick: Compared to Fio, Rumi is not willing to fight (and never wanted to do so in the first place), but Rumi is nice enough to help her fellow allies whenever she can.
* CuteClumsyGirl: Given the above. It's taken even further in ''3D'' when Rumi tries a dynamic entrance from a helicopter and screws it up.
* FanservicePack: Apparently, they've been starting to unbutton their shirts since ''Defense'', even though their sprites in ''Attack'' show them with their shirts buttoned all the way up.
* InSeriesNickname: "The Wandering Ghost"
* ItRunsInTheFamily: Both sisters being terrible with directions.
* TheMedic: Rumi is seen in the bad ending of ''Metal Slug 4'' taking care of the characters who got caught in the final mission's explosion. The Recovery Support in ''Metal Slug Attack'' represents her in a nurse outfit. She later turns into a CombatMedic in the 2.3.0 update. In the 2.5.0 update, Madoka is literally this, as her special attack heals the players units on the map.
* MotorMouth: In ''3D'', Rumi is very talkative, cheeky, and prone to going on tangents. She even sasses Marco after he gives her direct orders (she's a corporal; he far outranks her at Major).
* {{Mukokuseki}}: Let's be honest, they look even less Japanese than Eri.
* NoSenseOfDirection: Though they count as P.O.W.s, they are never caught by the enemy. They just happened to wander through the area.
* OlderThanTheyLook: Despite being a PaletteSwap, Madoka is eleven years older than Rumi.
* OutOfFocus: Rumi has had more game appearances and cameos than Madoka. In both tower defense games, Rumi is the one who generates AP in the field and gets playable status in ''Attack''. In ''Attack'' only, Madoka appears in the item support menu, but now appears as a playable unit alongside her sister in the 2.5.0 update.
* PaletteSwap: Madoka has brown hair and grey attire compared to Rumi's blonde hair and green attire.
* PintSizedPowerhouse: Both walk and carry an overly large backpack holding various ammunition and food items. Downplayed as they seem to be struggling to keep balance.
* SeriesContinuityError: ''Metal Slug 3D'' has Rumi ranked as a Corporal even though she's a Sergeant in every game she appears in.
* StunGuns: Madoka's close range attack in ''Attack''.
* TimedMission: If they are on screen long enough without being tagged, they will stop to salute and run away, not giving any credit to the player for rescuing them.
* UnusuallyUninterestingSight: Both sisters tend to wander the active battlefield without any care. It is not until they see one of the protagonists where they bail out of there.
* WimpFight: One-sided in ''Attack'', Rumi flails her hands rapidly if anyone gets close to her; [[FingerPokeOfDoom it's still enough to knock them out]].


[[folder: 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:

* GuideDangIt: Sometimes appears when the player hits a specific invisible spot multiple times.
* KamehameHadouken: His main attack has him fire a ''homing'' hadouken at enemies. It also deals pretty good damage too.
* ObfuscatingStupidity: He pretends to be a captured POW ''on purpose''. Once he's "rescued", however...
* ScrewThisImOuttaHere: Runs away once his rescuer dies.
* ShoutOut: [[Series/KamenRider His first name starts with the letter H, and his last name is Ichimonji]], [[NamesTheSame but he's no Hayato]]. Doesn't stop him from kicking ass though.

[[folder: 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

[[folder: Sophia Greenville]]

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

!! Sophia Tropes:

* AscendedExtra: While every instructor in the series shows up in ''Metal Slug Defense'', Sophia is the only one that hosts the Combat School in ''Attack'' (along with new sprites for her).
* BabiesEverAfter: Margaret, the instructor from Metal Slug X hints that Sophia retires to raise a family.
* TheBusCameBack: Shows up with Margaret in the second and third Pachislot games in Japan. In the West, it is in ''Metal Slug Defense''.
* 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.

[[folder: Margaret Southwood]]

The drill instructor of ''Metal Slug X'' and Gimlet's mission control in ''Metal Slug: Second Mission''.

!! Margaret Tropes:

* AscendedExtra: Unlike other instructors, she has given larger roles in certain games. In ''Second Mission'', she appears as mission control in the main adventure and even shows up in certain missions as the end goal. In ''Defense'', she hosts the game's events.
* ArtShift: ''Metal Slug Defense'' uses her sprites in ''X'' for the Events and her new artwork for the Combat School.
* DrillSergeantNasty: A jerk to you on the lower ranks, although she'll soften up as you rise among the ladder.
* EarlyInstallmentCharacterDesignDifference: Wore a green military dress in ''X'' before changing to a blue dress for ''Second Mission'' onward.
* EasterEgg: [[spoiler:Touching her breasts]] in ''Metal Slug Defense'' will cause her to react depending what rank you are in.
* EyesAlwaysShut: [[OOCIsSeriousBusiness If she opens them]], you've either impressed her, or you've made a complete ass of yourself.
* HairColorDissonance: It's uncertain if her hair is blonde or lightish brown but sometimes her hair is represented by a darker shade of brown.
* LikeAGodToMe: Hitting the Super Devil rank will make her admire you to the point of calling you "Her Majesty".

[[folder: Riviera "Lilly" von Wittenberg]]

One of the two drill instructors in ''Metal Slug 6''.

!! Lilly tropes:
* DrillSergeantNasty: Even moreso than the other instructors.
* FanservicePack: Shows more cleavage in ''Defense''.
* HairDecorations: Has a feather on her head.
* HairTriggerTemper: Most of the time looks calm until something provokes her.
* QuitYourWhining: Hates whiners and is often cold with them.

[[folder: Maryell "Mary" von Wittenberg]]

One of the two drill instructors in ''Metal Slug 6''.

!! Mary tropes:
* DrillSergeantNasty: Averted, she's much nicer and less stern than the other instructors.
* TheKlutz: Seen dropping her documents.
%%* YouGottaHaveBlueHair

!The Slugs

[[folder: 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.
* [=SV-000=] and the Proto 2, a less defensive prototype that is able to turn around.
* The Black Hound, a Ptolemaic-made variation the is remotely controlled and equipped with a laser and homing missiles.
* MS-Alice, an SV-001 inhabited by a sentient A.I. named Alice; created by Marco.

!!SV-001 Tropes
* AIIsACrapshoot: The Black Hound's an AI-controlled tank that goes rampant, attacking/killing its own Ptolemiac allies in the area before you face it.
** Averted with [=MS-Alice=], who is completely loyal to Marco for creating her.
* ArmoredCoffins: There's no way to easily bail out of the 000. Either you get out after defeating all enemies or letting it explode.
* 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.
* BonusBoss: Fighting the Black Hound is entirely optional in a secret area, and it gives no reward.
* 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.
* SuperPrototype: Ad advantage the 000 has over the 001 is the ability to turn around fairly easily. Unfortunately, the exit hatch is easily warped, making the thing into a deathtrap if it gets hit at all.
* SuicideAttack: Pressing Fire and Jump while in it will cause it to rush forward and explode.

[[folder: 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 useful 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 glacier.
* 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.
* {{Nerf}}: ''X'' makes some levels harder by replacing the SV-001 with the more awkward Slugnoid.
* 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.

[[folder: 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.
* TruthInTelevision: Camel-mounted machine guns actually existed in real life, called ''zamburaks''.
%%* WeaponizedAnimal

[[folder: 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, as well as Sidewinder missiles that fire directly forward. It's only variation is the Slug Jet, which is controlled by an NPC instead.

!! Slug Flyer tropes

* DavidVsGoliath: The fight between Slug Flyer and Shooting Ray in ''5'' shows that the Flyer is barely the size of a single engine of the Shooting Ray.
* HomingProjectile: Its 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.

[[folder: 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 eats a car battery.
* TrampledUnderfoot: It can kill a zombie merely by walking over it.
%%* WeaponizedAnimal

[[folder: 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
* ShoutOut: The Slug Sub is a direct recreation from the submarine from ''In The Hunt'', while the Slug Mariner is essentially a chibi ''Thunderbird 4'' from ''{{Series/Thunderbirds}}''.
* SuperPrototype: The Slug Sub is actually the ''prototype'' of the Slug Mariner, despite its more diverse moveset.

[[folder: Bradley Slug]]
A Regular Army variant of the common rebel M15 Bradley, that was stolen from the Regular Army.

!! Bradley Slug tropes

* CutscenePowerToTheMax: Jumping into it for the first times has the player turn the Bradley Slug around to face the correct direction, something that would be incredibly useful to do in game but is impossible for the player to do.
* GoodColorsEvilColors: Bright Green to represent the Regular Army, as opposed to the grey/dark green of the bad guys.
* GlassCannon: It houses one of the most powerful secondary fires available, but is very fragile
* HowDoIShotWeb: Despite being found in the hands of rebels, they don't have any idea how to work its vulcan cannon or its jumping ability, only knowing how to operate its indirect missile fire like their standard Bradleys.
* JumpJetpack: Is jumps with the help of a thruster beneath its treads.
* MercyInvincibility: Subverted. It receives no invincibility and can even be hit multiple times with the same bullet.


[[folder: Slug Gunner/Armor]]
The SVW-001 Slug Gunner and its variants are considered the final evolution of Metal Slugs. Walking on two legs for mobility, or on treads for speed, this type has the highest firepower but lowest speed of common slug types. Variants include the Proto Gunner, which is an quicker, unarmored version, and a multitude of mask-differentiated enemy variants. It is based on the rebel-designed LV Armor, which itself has variant branches of design in the more compact Slug Armor and the mass produced Ptolemaic Unit. The Ptolemaic Unit itself has four variants: Armor, Claw, Gunner, and [=MG=] (Machine Gun).

* AmbidextrousSprite: The Slug Gunner swaps its weapons while turning.
* AwesomeButImpractical: The LV Armor, unlike other slugs, requires ammo, can't shoot diagonally (some of them can do the heavy machine gun spreading motion), and takes one full second to jump makes it a liability at the worst of times.
* CloseRangeCombatant: The Ptolemaic Claw Unit is the only Armor to not have any projectiles at all, only using its fists. Conversely, the [=MG=] has only guns and no ability to melee.
* DenialOfDiagonalAttacK: The LV Armor has a major deficiency in its ability to shoot diagonally, which even applies to heavy machine gun ammo.
* DoubleJump: Most kinds can use rockets to boost itself once in the air.
* GatlingGood: One of the Slug Gunner's arm is equipped with a gatling gun.
* MiniMecha: They are mechas as large as the slug units.
* TransformingMecha: The [=SVW-001=] can morph between a Tank and a Mecha.
* PileBunker: The Slug Gunner has a pile bunker powered by revolving chamber.
* SuperPrototype: For those who prefer speed over mobility, the Proto Gunner is actually better.