The Neo-Martian, affectionately called Marty by the Professor, is a new character introduced in Metal Slug Attack.
Marty is the Neo-Martian, a powerful Mars People created by Rootmars. It was originally a normal Mars People with no special traits, but a burning desire to protect others from harm despite being weak.
After being transformed by Rootmars, Marty became much more stronger, and his desire to protect those who couldn't defend themselves grew. He is very good friends with the Professor, and although it had a rough start with Percier, also checks on her well-being. The lower-ranked Mars People admire him as a hero.
Marty is first seen in "Mad Scientists", where it accompanies Percier in saving the Professor after he is defeated by Navy.
He isn't seen after that until the second Christmas where it goes to Earth with Percier to make Christmas wish to bring the Professor back after he was killed by Abigail. Marty is initially terrified after sensing that Teleko is an Invader, but Percier convinces it to save one of the trees. However, they are too late and Teleko takes all the trees, causing Percier to cry. Marty later reassures Percier with the Professor's own words as they make their wish.
Marty later partakes in an operation on Earth to protect the environment from the humans, obtaining new Gigantalos equipment and is accompanied by Tank. They encounter Growl, who challenges them to a fight. Both Marty and Tank are somehow able to sense he also wants to protect the Earth, and accept his challenge to see if he is capable of doing so. Growl defeats the two Martians, and they realize his soul is pure-hearted during their fight. They depart Earth, bidding farewell to the noble warrior and promising not to lose next time.
Marty is first seen in "Utopia", where it is a lowly Mars People who watches the Professor request to join the Martians. However, he is seemingly denied and warped back to Earth. The Professor notices it and manages to start communications, and it reveals to him that Rootmars did not deny him, but did not accept either. Instead, Rootmars will allow him to join if he can prove his strength to the Martian leader by acquiring the Sun Stone. The Professor makes his way to the temple where the stone is housed, while the Mars People accompanies him.
Marty runs into several Samurai Infantry but eludes them, before saving the Professor from brainwashed Rebel soldiers. The Professor begins to collect samples, gaining the Martian's attention. The Professor tells it that researchers never give up. They soon come across a LV Armor, and the Martian sacrifices its life to protect the Professor. The Martian enters a trance where after having a nightmare and remembering the Professor's words, turns into Mars People Neo and assists the Professor in destroying the Sol Dae Rokker. After the battle, the Professor is accepted by Rootmars and he decides to start naming the Martians, finding it annoying that they don't have names. He gives Mars People Neo the name "Marty".
Marty is later kidnapped by the Rebel Army and used to power the Big Gate. The Martians are aware of his disappearance and thanks to the Professor, they track him down to the facility where the gate is being powered. Marty telepathically communicates with Percier, glad it has made a new friend, but Percier shuns it since the Professor abandoned her for them. Though freed, but severely weakened, Marty manages to pull enough power to destroy the Kraken before being returned to the Rugname, where it recovers.
The Professor creates new equipment for the Martians and a group of three Mars People compliment the equipment he has made. Marty drags one of them away to test the equipment, and after it is a "success", the other two voluntarily join in. After the Martian Rangers have a near-death experience and return to the Rugname, Marty is in a bind for dragging them into danger, but Percier sends it flying to them after it is unsure of what to say. It attempts to apologize to them, but the Martian Rangers tell it that it felt good to protect others for a change.
While on break, Marty watches as Percier is trampled by a Mars Mecha. When she yells at Clone Abby to look out for her too, it responds that it is not inclined to. Percier begins crying, and Marty attempts to reassure her.
Marty is later on patrol when he notices some Martians have stopped communicating and investigates. It encounters Dion and challenges the lieutenant to a fight. The two are evenly matched, but Marty eventually realizes something is wrong when Dion doesn't attempt to flee after destroying his jamming device. A normal Mars People tells him the Professor is in danger, but Dion stalls him long enough that Abigail is able to kill the Professor, or so they thought.