Zero (Mega Man)
Zero (ゼロ, Zero) is a central character in the Mega Man X sub-series of the Mega Man universe, and the protagonist of the Mega Man Zero sub-series.
Along with X, Zero was one of the first robots to have complete free will and thinking capabilities of a human, known as Reploids. It was revealed in Mega Man X4 that he was created by Dr. Wily to destroy the original Mega Man, but was too unstable and violent to be controlled, forcing Dr. Wily to seal him in a capsule. Later, in the year 21XX, a group of Maverick Hunters found Dr. Wily's lab and released Zero. As he still wasn't cured of his violent nature, Zero defeated those Maverick Hunters, causing him to be labeled as a Maverick and forcing the then-leader, Sigma, to fight him one-on-one. Zero lost the fight, but he also became stable from his Maverick-like state after the duel. On the other hand, Sigma was infected with the Maverick Virus, causing a change in roles between him and Zero. Zero joined the Maverick Hunters, becoming an S-rank Hunter as well taking the role of a mentor and friend to X.
After Sigma was finally defeated once and for all, Zero and X were involved in a new conflict called the "Elf Wars" due to its use of the electronic life-forms known as cyber-elves. Zero, having learned that his code was the original source of the Maverick outbreak, went into hybernation while scientists worked on a way to remove the malicious code. In that time, he was given a second body to inhabit, which he was awakened in by the human scientist Ciel, seeking his aid to defeat her rebellious creation, a copy of X. While Zero helps with the resistance group that Ciel leads, he soon learns that his original body had been stolen by a mad scientist named Dr. Weil, naming the original body as "Omega". Zero destroys Omega and later defeats Weil, despite knowing the fact that he was human too, putting an end to the Robot Wars that Wily had begun centuries ago.
In Ultimate, all of the techniques Zero uses as an Assist Trophy originate from the Mega Man X series:
Zero's double jump and air dash, which he uses in Ultimate, were originally special techniques in Mega Man X4, known as the Kuenbu and Hienkyaku (respectively), that had to be obtained by defeating Mavericks (Split Mushroom and Jet Stingray). In later games, however, they have been available to him from the beginning.
As a costume
Zero's trophy is exclusive to the Wii U version, under the name "Zero (Mega Man)" for disambiguation.
A close friend and mentor to X, Zero first appeared in Mega Man X. He's a Rank SA Maverick Hunter and is capable of instantly learning new moves from his enemies. Zero has great faith in X's hidden potential, and together they fight to take down Sigma and defeat his rebelling forces.
As an Assist Trophy
Zero appears as an Assist Trophy character. Upon being summoned, he says "Fight's on!" and chases opponents to attack them using a variety of techniques:
Much like in his series, Zero has a double jump, and can move with high-speed dashes both on the ground and in the air. He is also one of the Assist Trophies capable of performing directional air dodges. For all his techniques except the triple slash, Zero shouts their names when using them. He will then say "Back to base!" when departing. He also can be defeated, when he is defeated he gets blast KO'd but also explodes into orange orbs, a reference to his death animation in some of his appearances.