Setting The first game's story involved the Peregrine Falcon (PF) Squad, a small but skilled team of soldiers serving under the Regular Army's special operations division, who fight against the army of General Donald Morden in order to prevent a massive coup d'état and the creation of a New World Order. Later games featured characters from the Sparrows Unit, which is under the control of the Regular Army's intelligence division. Beginning with
Metal Slug 2, the PF Squad also battles an alien threat to Earth (the Mars People), as well as several other supernatural threats including
yetis,
zombies, ambulatory Venus flytraps, giant crabs, and
mummies. These outlandish elements were removed from the fifth game to return to the feel of the original title. The fifth moved to the motif of modern guerrilla warfare, leaving only traces of the series' signature quirky humor and paranormal enemies, with the exception of the final boss.
Metal Slug 6 returned to the plot of the first three installments, bringing back Morden's Rebel Army and the Mars People.
Metal Slug 7 has less outlandish elements with the Mars People replaced by an alternative universe of Morden's Army with futuristic equipment and weapons.
Characters Heroes Major Marco Rossi (voiced by Takenosuke Nishikawa in
NeoGeo Battle Coliseum and by
Kenta Miyake in
Neo Geo Heroes: Ultimate Shooting) and
Captain Tarma Roving were the only playable characters in the first game, and each was reserved solely to the first and second player, respectively. From the second installment, characters can be chosen independently, and
Sergeant 2nd Class members Eri Kasamoto and
Master Sergeant Fiolina "Fio" Germi were added to the cast. These four are typically considered to be the quintessential
Metal Slug team. In the fourth game, Nadia Cassel and Trevor Spacey made their debut, replacing Eri and Tarma. They have not returned in later games, as they were created by the Korean-based Mega Enterprise and due to Playmore retaining intellectual rights to all SNK titles. Eri and Tarma returned in the fifth game. The Game Boy Advance edition of the game features two new characters specific to that title: PF squad trainees
Cadets Walter Ryan and Tyra Elson.
The King of Fighters/
Ikari Warriors characters
Colonel Ralf Jones and Second
Lieutenant Clark Still have appeared since
Metal Slug 6, and their
King of Fighters teammate
Leona Heidern is available as an extra downloadable character for
Metal Slug XX, a revised edition of
Metal Slug 7.
Enemies General Donald Morden is the main
antagonist of the
Metal Slug franchise. He is depicted as a rambling madman wearing a beret, eyepatch, and wearing his army's uniform. In some games, he bears a passing resemblance to
Saddam Hussein. He appears in every game except
Metal Slug 5. He apparently mends his ways by the end of
Metal Slug 6, as he (or Rootmars depending on the player(s)' chosen route) rescues the player(s) after they are knocked off a wall by an explosion caused by the alien end boss. His army is the main force of opposition in the
Metal Slug games, with the exception of
Metal Slug 5 and
6. He commands the Rebel Army, and in
Metal Slug 4 he was thought to be behind the Amadeus Terror Syndicate. He once again returns to his roots of attempted world domination in
Metal Slug 7, this time with the help of the Rebel Army from the future, also being the final boss for the first time since the original
Metal Slug. Like the main characters, General Morden appears in various SNK games as a cameo, especially in the
SNK vs. Capcom: Card Fighters series. Allen O'Neil, a sub-boss, appears in all of the games except
Metal Slug 5 and
6. He returns in
Metal Slug 7. He uses an
M60 machine gun, a knife, and grenades. Despite the fact that Allen is clearly killed at the conclusion of every encounter, the game makers have humorously brought him back in each new iteration of the series. Allen's son, Allen Jr., appears in
Metal Slug Advance as the recruits' drill sergeant but later reveals himself as a double agent for the Rebel Army. He can be fought in the final mission as an optional boss. The Mars People are aliens that are in a plot to take over Earth in the
Metal Slug universe. They resemble squids, using their tentacles as a form of movement, and a strange fighting style that involves gas and a laser pistol. In
Metal Slug 2, they appeared as enemies near the climax of the game, with their mother ship appearing as the final boss. They appear again in
Metal Slug 3, abducting Morden and one of the members of the Regular Army in the final level (whichever one the player uses will be abducted), only for the Regular Army and Morden's army to take the fight to their mother ship and defeat them, and their leader Rootmars. In
Metal Slug 6, the Mars People, Morden, as well as his rebel army, and the Ikari Warriors, join forces with the Regular Army to fight a new alien invader who feeds on the Mars People. In
Metal Slug X they appear as enemies early in the game. Mars People also are the first characters from the
Metal Slug series who appear in a fighting game: first in
SNK vs. Capcom: SVC Chaos as a hidden (but playable) character, and later in
Neo Geo Battle Coliseum as an unlockable playable character. == Development ==