Initially there was only four notable characters in the first game (Marco Rossi, Tarma Roving, General Donald Morden and Allen O'Neil). Later games feature new characters; some of them come from other SNK games.

Here is a concise list of the notable characters in the series.

Characters from Metal Slug Attack can be found here.

Heroes

Sprite Character Debut
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Marco Rossi: A Major of the P.F. Squad.
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Tarma Roving: A Captain of the P.F. Squad, and a good friend of Marco.
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Eri Kasamoto: A Sergeant of the S.P.A.R.R.O.W.S.
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Fio Germi: A Major Sergeant of the S.P.A.R.R.O.W.S.
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Trevor Spacey: A Sergeant of the P.F. Squad.
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Nadia Cassel: A Private of the S.P.A.R.R.O.W.S.
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Ralf Jones: A Colonel of the Ikari Mercenaries Squad.
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Clark Still: A Major of the Ikari Mercenaries Squad.
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Leona Heidern: A member of the Ikari Mercenaries Squad.
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Walter Ryan: A cadet of the P.F. Squad.
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Tyra Elson: A cadet of the P.F. Squad.
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Roberto Nicola: A member of the P.F. Squad.
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Nathalie Neo: A soldier of the Regular Army.
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Alisa Stewart: An Engineer of the Regular Army.
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Hero: Unnamed soldiers of the Regular Army.
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Gimlet: A member of the P.F. Squad.
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Red Eye: A member of the S.P.A.R.R.O.W.S.
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Tequila: An agent of the Regular Army.

Support Characters

Sprite Character Debut
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Hyakutaro Ichimonji: A POW that can fire energy balls from his hands. He is a Second Lieutenant of the Regular Army.
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Rumi Aikawa: A Sergeant of the Regular Army.
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Madoka Aikawa: Rumi's elder sister and a Private of the Regular Army.
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Utan: A specialized orangutan that uses an Uzi. He is a mascot of the Regular Army.

Villains

Sprite Character Debut
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Donald Morden: The main antagonist of the series. He is the leader of the Rebel Army.
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Allen O'Neil: An immortal Elite Soldier of the Rebel Army. He is famous for appearing in successive games despite apparently being killed in each game he appears.
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Abul Abbas: Leader of the Arabian Infantry and affiliated to the Rebel Army.
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Rootmars: The leader of the Martians which are occasionally affiliated to the Rebel Army.
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Doctor: Scientist leader of the Amadeus Syndicate and affiliated to the Rebel Army.
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Ptolemaios: Leader of the Ptolemaic Army. Originally supposed to debut in Metal Slug 5.
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Avatar of Evil: A demon-like entity that came to Earth and is the presumed leader of the Ptolemaic Army.
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Invader King: The leader of the Invaders.
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Allen Jr.: The son of Allen O'Neil. He is a Spy and an Elite Soldier of the Rebel Army.
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Oguma: Leader of the Oguma Corporation and affiliated to the Rebel Army.
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Lt. Colonel Macba: The Lieutenant-Colonel of the PHANTOM Squad of the Rebel Army.
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Hilde Garn: Colonel and Commander of the PHANTOM Squad of the Rebel Army.
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Lt. Wired: Second-in-command of the Rebel Army's PHANTOM Squad.
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Kanan: Commander of the PHANTOM Squad.
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Unknown Alien: An alien lifeform that came to Earth and made a nest. It's unknown where it came from.

Other Characters

Game represents their first appearance.

Combat School Instructors:

NPCs:

Pachinko Characters:

Mobile Characters:

Unused Characters:

Characters
Heroes Main Series Marco Rossi | Tarma Roving | Eri Kasamoto | Fio Germi | Trevor Spacey | Nadia Cassel | Ralf Jones | Clark Still | Leona Heidern
Spin-Offs Walter Ryan | Tyra Elson | Hero | Gimlet | Red Eye | Tequila
Mobile Roberto Nicola | Nathalie Neo | Alisa Stewart | Helton | Tilde | Nikita | Matilda | Amir | Whip | Heidern
Support Hyakutaro Ichimonji | Rumi Aikawa | Madoka Aikawa | Utan | Navel | Selina | Issenman Tarou | Eris | Hyakumantaro | Pupipi
Villains Main Series Donald Morden | Allen O'Neil | Abul Abbas | Rootmars | Doctor | Avatar of Evil | Invader King
Spin-Offs Allen Jr. | Oguma | Macba | Lt. Wired | Kanan | Hilde Garn
Mobile Unknown Alien | Victor | Ptolemaios | Anubis the Chained | Nanook
Instructors Sophia Greenville | Margaret Southwood | Riviera von Wittenberg | Maryell von Wittenberg | Cynthia Hartnett | Anne
NPC Announcer | POWs | Duke Koudou | Satiko Suzuki | Gerhardt City Civilians | Scott Amundsen Jr. | Miner | Genie of Lamp | Orca | President | Survivors | Fishman | Lumberjack | Sailor | Chinese Soldier
Crossover KOF Team | Battle Cats
Unused Phil Gene | Michiko Nakajima | Angry Man | "Achilles" | "Tabomba"
Metal Slug Attack
Regular Army Associates MS-Alice | Anna Wiese | Midori Schumann | Mello | Rita Lewinsky | Amber | Nikita | Reika Bradford | Louise | Gisee | MS-Heart | Ashley | Rocky | Growl | Jephet | Victoria | Claudia | Kanae | Howell | Phi | Karen
Metal Device Project Perche | Ami | Molly | Menzel | Ulala | Maggie | Avvio | Quaith
Rebel Army Associates Rapid | Julia | Chloe | Izabella | Edda | Growth & Cline | Naomi | Alesha | Jane Doe
ACE Abigail | Dion | Romy | Kriemhild | Katalina
"Frozen Brigade" Beatriz | Vicky | Dolores
Blaze Brigade Grazia | Loretta | Norah
Allen Platoon Destrade | Huracan | Conny | Nantes | Padwah
Science Department Vita | Navy | Nova | Emma | Millefie | Sylfie | Fluffy
Arabian Army Shizuka | Aisha
Ptolemaic Army Rebellion Dragunov | Yoshino | Caroline | Veronica | Sisilia | Towa | Simon | Miharu | Chunyan | Owen | Sho | Lucy | Phoebe | Josette | Mizuna | Matilda | Little Lady Black | Svetla | Humphrey | Lithos | Yutong | Tatyana
Cultists Mira D. Genesis | Maria | Damian | Achetto | Sally | Cara | Oao-One | Sorceress
Secret Sect Anastasia IV | Believers | Beecham | Melvina | Anastasia I | Zahara
Space Army Martians Professor "Aionion" | Mars People Neo | Percier | Clone Abby | Clone Betty | Mars People Rangers | Ariadna | Gemini Twins | Halle | Bonny | Clario | Harriot | Code Marionette:Un | Pauline | Leone | Claris | Unsigned
Invaders Odette | Annette | Lydia | Nowan | Schwarz Metzelei | Fedeln Metzelei | Rillacle | Franke | Teleko | Bloom Metzelei | Odile | Bersek | Geweih Metzelei | Purple King | Barbeln | Biene Goldenes | Swordeist | Drache Goldenes | Eis Monstrum
Independent Army Amadeus Syndicate White Baby | Alma | Iron Fortress | Valerian Bears | First Baby | Type:Ant-Lion
Red Goblin Society Scotia Amundsen | Red Goblin | Vatn | Jin | Aileen | Elena | Licht | Ichima | Wendy | Bushin Tenzan
Mummy Army Pharaoh | Cleopatra | Hemet | Arsinoe | Hathol | Sharifa | Ramal | Sekhat
Vampires Aswang | Agalia | Sharl | Grace
"World Military Corp." Kelly | Maya | Mirror Mantis
Mirage Circus Cocatrix | Bunny
Independents El Dorado | Elysion | Esther | Teresa | Minerva | Yang Dao | Otto | Yuki Tsuki Hana | Ido
Gameplay Elements
Screens Status Screen | Continue Screen | Game Over Screen | Recaptured Prisoners | Best Tank Busters | Arcade Settings
On-Screen Elements Items | Weapons | Slugs | POW | Characters | Enemies | Military Vehicles | Bosses | Environmental Objects | Civilian Vehicles | Rank Medal
Actions Metal Slug Attack | Vulcan Fix | Transformations | Metallish System | Rush Blaster System | Weapon Stock | Deaths | Invulnerability | Canceling | Super Devil Mode
Modes Combat School | Another Story | Another Mission | Storming the Mothership | Fat Island | Office
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