Allen O'Neil

Allen O'Neil is a character from Metal Slug series, he makes his debut on the first Metal Slug game as a Sub-Boss on Mission 3.

Profile
Allen is one of the main soldiers in the Rebel Army, and a recurring mid-boss in most Metal Slug games. Despite seemingly dying after every battle, he consistently reappears at full strength, and as such, is often considered "immortal". You can battle his son, Allen Jr. as an optional boss in Metal Slug Advance.

Allen is infamously known as the "Immortal Devil Sergeant", as even though he is constantly killed every game, he manages to survive every attempt on his life.

Metal Slug Appearances
Metal Slug 8 (Ratbrute)

Allen is a playable character in Multiplayer mode only.

Metal Slug 8 (TheProjectXZoneFan1997)

Allen appears as a boss on Mission 1 riding an upgraded model of his Rebel Giant, he is also a temporal ally on Final Mission killing some Zombies from the base.

Metal Slug 8 (Lord Moogoo)

Allen appears in an opening cutscene where he saves General Morden from a stray rocket about to hit him. His whereabouts were not known afterwards. An upgraded robot version (Cyborg Allen O Neil MK.II) of himself was found deep in Amadeus's Space Satellite Cannon later on, again pretending to be the real Allen.

Metal Slug 1X0

Allen appears as a boss in Final Mission.

Metal Slug 11

He is a boss on Mission 1 riding an upgraded version of Bull Drill.

Metal Slug 12

Allen appears as a boss on Final Mission teaming up with his disciple Destrade.

Crossover Appearances
Metal Slug vs Aliens

Allen appears as a Boss on Mission 3.

Project X Zone 3: Sacred Destinies

Allen appears as a Boss Unit, he join forces with Ouma and Shadowloo to secretely stole their plans to use them for Rebel Army's Multiverse domination but his plans got foiled by PF Squad soldiers Marco Rossi and Eri Kasamoto, the Metal Slug events in Project X Zone 3 took place after Metal Slug 7/XX and before Metal Slug 8 (AStranger195)/Metal Slug 8 (Ratbrute)/Metal Slug 8 (TheProjectXZoneFan1997).

Super X Dimensions

Allen appears as a Boss Unit.

Divine X Union

He appears as a Boss Unit.

Neo Geo 2: Match of the century

Allen makes a Cameo appearance on Akari's Shikigami Hyakkiyakou/100 Demons' Night.

Trivia

 * Allen is the only character in the entire series to have spoken dialogue, while all other characters only have laughs and screams including a catchphrase.
 * 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 Metal Slug Mobile 3 (Remake).
 * Based on Metal Slug Defense description of Cyborg Allen unit, the Cyborg Allen that appear in Metal Slug 4 is the real Allen who has retired after enduring serious injury.
 * On Metal Slug Attack SNK rename it to "Mecha Allen" and change the description completely for unknown reason, because of this change in Metal Slug Attack, "Mecha Allen" is Described as a Robot that based on Allen O Neil data. with improved resistance
 * His Haircut and Beard may resemble towards Russian Leader of Leningrad, Vladimir Lenin.
 * His gun is not actually an M60, instead it's an M240 Bravo.