The Mars People are enemies that appears in the most of main series.
The Martians are would-be alien invaders and have aligned with the forces of General Morden to use them in order to weaken the Earth's military forces. After they reveal their true plan, the Rebel Army makes a temporary alliance with the Regular Army to stop the Martians.
Mars People have a large head with multiple tentacles placed below. Their tentacles are fairly strong; they can hold a weapon using only one of their appendages. Contracting their tentacles allows them to jump large distances and descend slowly.
According to their death animations, Martians possess a skull and green blood. Some artwork shows them to have mouths. The Game Over screen of Metal Slug 6 shows the skull of a Mars Person, revealing them to also have teeth and a nasal cavity. The skull appears to be made of bone. Severed tentacles writhing about after dismemberment suggest an involuntary nervous system.
Sprites imply they have hollow heads. Artwork has them with full heads with a puncture below.
Their weapon of choice is a gun that can fire varying types of spores. These spores are destructible by knife and gunfire.
Mars People's names are mostly formed with the syllables Pa-Pe-Pi-Po-Pu (except Rootmars and Marty). These syllables also form the Martian Language, and a translation device is required to understand them.
|Mars People: The most commonly seen, and likewise the weakest.|
|Mars People Cadre: Stronger than the regular one, but slower.|
|Mars People Elite: Faster than the regular one, and stronger than Cadre members.|
|Mars People Pocket: Appeared in Metal Slug Defense / Metal Slug Attack as part of new year celebrations. Their sprites are based on those from Metal Slug: 2nd Mission. One of them, named "Pocke", accompanies Halle in Metal Slug Attack.|
|Party / Halloween People: Likewise seen in Metal Slug Defense / Metal Slug Attack, these are Mars people who wear disguises to integrate into human society.|
|Mars People Neo: The strongest of the Mars People, created by Rootmars during one of the stories in Metal Slug Attack. He is affectionately nicknamed "Marty" by the Professor.|
|Percier: A young girl who dresses as a Mars Person in Metal Slug Attack. Not actually a great fan of aliens.|
|Mars People (Gray): Drives the Mini-UFO in early versions of Metal Slug Defense, though the pilots were later changed to regular Mars People. Also seen in some other mobile games (which?).|
|Mars Morden: A Mars Person disguised as Donald Morden, appearing only in Metal Slug 3. When uncloaked it appears as a regular Martian, albeit with an eyepatch.|
|Mars People Officer: Can summon Fake Rootmars to attack. Appeared in Metal Slug Attack.|
|Mars People Officer (COO): A stronger variant of the original officers. Their guns can create a stronger portal for Fake Rootmars to absorb attacks. Appeared in Metal Slug Attack.|
The Mars People appears as a hidden playable character and mid-boss. He attacks using his tentacles and his gun, and can also call a traditional Japanese-style UFO. His attacks are named after paranormal folklore, such as the Tunguska Blast of 1908 and the Roswell incident.
He appears again as a playable character, with little different than his SVC counterpart. A Mars People model is available in a variety of different colors.
- Like many parts of their forces, Mars people themselves have some visual basis on the Martian invaders from H.G. Wells' literary classic "War of the Worlds", where they are originally described as cephalopods with psychic abilities.
- The Mars People also have some basis on the common depiction of Martians in Japan. While in western culture Martians are green-skinned humanoids, in Japan they are depicted as octopi.
- In the first mission of Metal Slug X, when you destroy the barricades, you can see burning Martian corpses being thrown out of the blast.
- In Metal Slug 6, the spore which Martians fire is the same as the captain, but travels slower.
- The Ptolemaic cultist shoot what resembles Martian spores from their pistol.