Metal Slug Wiki
Metal Slug Wiki

"See you in hell..." - Allen's famous "last" words.


Allen O'Neil is one of the main soldiers in the Rebel Army, and a recurring mid-boss in most Metal Slug games.

Allen is infamously known as the "Immortal Devil Sergeant", as even though he is constantly killed every game, he somehow manages to survive with little injury to himself.


Allen approaches the battlefield in a hot-headed and insulting manner when it comes to fighting the soldiers of the Regular Army. Allen loves fighting the enemy, and it is why he prefers to remain as a sergeant because it is the highest rank possible that allows him to fight in the front lines on a daily basis.

His sheer strength is matched by far of his ego, often slagging and making comments about his enemies. While his superiority complex does get the better of him, he is an adept soldier, capable of enduring more punishment than his weaker comrades.

The only thing that keeps Allen alive, besides his muscles and big-head, is his devotion and will to return home to his wife and son[1]. Players can battle his son, Allen Jr. as an optional boss in Metal Slug Advance.


Allen O' Neil was the most trusted soldier from Donald Morden while he was a commander in the Regular Army. When Morden started his rebellion, Allen followed him out of loyalty, helping him in his coup d'état against the Regular Army.

Metal Slug

During the Regular Army's operation in the Käthehirt Valley to destroy Rebellion motor pool, he single-handedly slaughtered the incoming Regular Army troops as they climbed up the mountain. He was ultimately defeated and believed to be dead.

Metal Slug 2 and Metal Slug X

Allen reappears again to fight on the bridge to the Rebel Secret Base. He always has two Rebel soldiers to help him in the fight. Defeated, he falls off the cliff and is promptly eaten by an Orca.

Metal Slug 3

Allen is the first mid-boss of Mission 5, controlling a Hairbuster Riberts, and was defeated again. Later in the same level, when the heroes are making their escape from the crumbling Rugname, Allen shows again, this time to give support fire for them, but only if the player is not in possession of the Metal Slug.

Metal Slug 4

Allen appears in the second boss fight, controlling the Toschka Dalanue. After the tower is destroyed, he is thought to be defeated. Notably, this is the first time in the series that Allen serves as an end-of-level boss, as opposed to his usual mid-boss status.

The commandos fight him again in a factory, though he is revealed to be a robot created by the Amadeus Syndicate, which was also responsible for creating Morden Robots. The presence of Morden Robots led the general public to believe that Morden was also the leader of the Amadeus Syndicate.

Metal Slug 7 and Metal Slug XX

Allen once again shows himself in Mission 6 riding a Rebel Gigant. As the player faces him in a Slug Gigant, Allen is once again defeated.

Metal Slug Attack

Allen appears in Metal Slug Attack as a playable unit in multiple incarnations; standard, enraged, and using the Rebel Gigant. A variant called "Immortal Allen" has him sport new weapons every time he's enraged from his M240 while driving a jeep, to a large bazooka, and finally holding a large buzz saw.

He also appears in the Another Story mode in multiple stories.

Allen is in command of the "Allen Platoon", the most violent division in the Rebel Army who are often the most wounded after an operation due to their love for fighting. Allen has several officers under his command; the only known officer in Allen Platoon is Destrade. Other notable members include Huracan, Conny, and Nantes.

His robot counterpart also appears numerous times, primarily manning the Toschka Dalanue and a few other machines.

Metal Slug 3D

In this game, Allen first appears in a cutscene where he leads an army of Di-Cokka's to attack a Regular Army base in the middle of a desert. When Tarma, FioEri, and several Regular Army soldiers try to fight off these invaders, they eventually get defeated as the Di-Cokka's destroyed many Slug tanks and killed Fio and Eri by blasting them to bits. Later on, in the underground ruins, Marco confronts Allen trying to blow up the ruins with a gigantic drilling machine but luckily he was able to disable it from exploding. Allen then orders his men to blow up the ruins with Marco in it with dynamite barrels, but all of his men get annihilated by a revived Eri (who was disguised as one of his goons). Angered, Allen shoots a load of dynamites before retreating hoping it'll blow up Marco and Eri but the two of them were able to run out of the way in time.

At the enemy base, Morden calls in Allen to eliminate Marco, Tarma, Eri and Fio before the four could apprehend him. Allen fights them, only to be defeated once again.


His design may have been based on the 80s action hero John Rambo (played by Sylvester Stallone), due to him being half-naked and armed with a heavy machine gun similar to the character in Rambo: First Blood Part II.

His M240 Bravo Machinegun is one of the two real modern Firearms in the Rebel Infantry (as opposed to their other weird mix of German WWII rifles and futuristic Weapons), the other being the AR-10.


"YAHAHAHAHA!" -Allen O'Neil

"Come on, Boy!" -Allen O'Neil

"Go home to mommy!" -Allen O'Neil

"You're mincemeat!" -Allen O'Neil

"See you in hell...!" -Allen O'Neil


In Metal Slug, Metal Slug 2/X, and Metal Slug 4, Allen fights in an arena composed of four platforms: two pairs are on each side with the top platforms being longer than the bottom two. Allen navigates the fight by hopping between platforms or running at the center floor, executing four actions, depending on distance:

  • His main attack is firing his M240 in quick, silent bursts. He can also aim it diagonally upwards, which is very deadly if on the upper platforms.
  • His secondary attack is throwing fast and flashing Pipe bombs when the player is out of range, accompanied by a random quote.
  • His melee attack is slicing the player when close in distance.
  • He'll move around to avoid continuous damage. When the player or their projectiles are near him, he'll attempt to back away.

After he is killed, he will fall to the ground, drop his M240, and utter his famous phrase. In Metal Slug 2/X, Metal Slug 3, and Metal Slug 4, the dropped M240 can be picked up and acts as a Heavy Machine Gun.

Mecha Allen plays similar to the real Allen except he gets more aggressive in his second phase. His melee attack does not kill the player; instead, the player is knocked a great distance and loses their weapons.


  • Allen is the only character in the entire main series to have spoken dialogue, while all other characters only laugh and/or scream.
  • His son Allen Jr. borrows some of his lines in Metal Slug Advance.
  • Allen is playable character and the protagonist of the games Metal Slug: Allen's Battle Chronicles and its remake, Metal Slug Mobile 3.
  • His haircut and beard resembles the Russian Leader of Leningrad, Vladimir Lenin.
  • Even though Allen does not appear in Metal Slug 6, the fight against the Controller bears similarities both in the arena design and the enemy actions by distance.
  • The player can manipulate his actions and even lock him in place by firing rounds at the ground in front of him[2].



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 | Elizabeth Mariani
Metal Device Project Perche | Ami | Molly | Menzel | Ulala | Maggie | Avvio | Quaith | Karen
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 | Draco
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 | Ai Agate
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
Metal Slug Tetsuyuki | Hairbuster Riberts | Tani Oh | Shoe & Karn | Iron Nokana | Hi-Do

Mini-Bata | Allen O'Neil

Metal Slug 2/X The Keesi II / Iron Nokana MK II (X) | Aeshi Nero | Dragon Nosuke | Big Shiee | Hozmi | Rugname

Mosque Artillery | The Keesi II (X) | Karn (X) | Allen O'Neil | Dai-Manji

Metal Slug 3 Huge Hermit | Monoeye UFO | Jupiter King | Sol Dae Rokker | Rootmars

Twin Ohumein-Conga | Monoeyes | Hairbuster Riberts | Hi-Do | Rugname | Fake Rootmars | Clone Incubator

Metal Slug 4 Brave Guerrier | Toschka Dalanue | The Iron | Big John | Sea Satan | Amadeus Mother Computer

Mecha Allen O'Neil

Metal Slug 5 Metal Rear | Shooting Ray | Screamer | Sand Marine | Avatar of Evil

Black Hound | Stone Turtle (unused) | Gaia Elephant | Ptolemaios (unused)

Metal Slug 6 Bull Drill | Iron Sentinel | Brain Robot | Elder Centipede | Invader King

Invader Controller

Metal Slug 7/XX Worm Mecha | Crablops | Destroyed Crablops | Fall Mecha | The Union | Rebel Gigant | Kraken

Scrap Tower | Big Gate

Metal Slug: 1st Mission Rebel VTOL | Rebel Train | Macba | Rebel Zeppelin | Electromagnetic Crane | Weapons Port Boss | Hilde Garn

Facility Elevator | Macba | Rebel Truck

Metal Slug: 2nd Mission Big Bertha | Terrain Carrier | Rebel Reactor | Macba | Rebel Submarine | Tani Oh | Wired | Rebel Airplane | Hilde Garn's Slug | Rocket UFO

Power Generators | Rebel Rocket | Hyakutaro

Metal Slug Advance Formor | Emain Macha | Kaladgolg | The Keesi III | Cabracan

Allen Jr.

Metal Slug 3D Parachuetruck | Mosque Artillery | Spider-Bot | Underground Cruise Missile | Morden's Battleship | Morden's Castle | Allen O'Neil | Lugus | Lieu
Metal Slug Attack Pharaoh's Arc | Ptolemaios | Ball Slug | Great Mother | Mars Gigantalos | K-O3 Coupled Armored Vehicle | Land Blowfish | Cyclobster | Slug Square | Zoni Doloma | Quadro Jumper | Denturion | D-Gu | Fortmeranian | Rock Mole | Giant Copter | Et A Omnis | Vortex | Digger Base | Crusty Legs | Armored Crawler | Queen Big Snail | 7000 Class Locomotive | Riviere Hyll | Metal Fusioner No.223
Mobile games Rocket Control Room | Unknown Alien | Hellfire | Spiderbot | Cyclops | Mega Laser Turret | Mars Battle UFO | M-32 Water Carrier Plane | Kourai | Alien Floating Structure