Rootmars

Rootmars is the leader of the Mars People, a alien race who wishes to conquer our world, the main antagonist in Metal Slug 3, as well as a controllable vehicle in Metal Slug 6.

Story
The Rebel Army, led by Donald Morden, made contact with him and Rootmars backed them up with their technology and resources to take over the world. However Rootmars was only using the rebels, so all of Earth's military forces would be weakened from suscessive battles, making it easier for the martians to fight any opposition. Morden is abducted by the martians and held in their mothership, so the Rebels make a temporary allegiance with the Regualr Army soldiers to fight the martians. Their mothership is severely damaged, so they retreat temporarily.

Rootmars immediately took the next step, abducting General Morden and sending a martian disguised as him to lead the rebels and start a new coup d'etat, causing numerous supernatural phenomena throghout the world. As the martians were unmasked, they kidnapped one of the Regular Army members and immediately made their escape, but they were followed by the rebels and the Regular Army. Their ship Rugname was invaded and Rootmars, who was controlling the ship using his brainpower, was put out of commision, thus triggering the self destruction of the ship. As the heroes made their escape from de blowing ship, Rootmars made a last attempt to kill them, but was ultimately defeated and sank to the bottom of the sea.

As Vehicle
Rootmars reappeared in Metal Slug 6 along with Mars People, they were attacked and preyed by Venusians. Therefore, it stroke a temporary alliance with the heros, allowing himself to be controlled as a vehicle in Stage 4, and eventually became one of the two possible being who saved the heros from a bottomless pit besides Morden, if the hero chose to ride Rootmars.