The famous, prestigious scientist known as Gate was a leading researcher of Reploid engineering who was fascinated by the mysterious nature of X and Zero's bodies and sought to analyze them, or at least to create comparable works. The resulting experiments were praised as ahead of their time, yet tended to be unanalyzable and misunderstood, leaving Gate to lead a secluded life. This nevertheless drew jealousy from some of his colleagues, leading to the Reploids he created being either sabotaged or labeled as Mavericks, resulting in their destruction and his departure from the team.

Following the destruction of the space colony Eurasia, Gate would visit the crash site and come upon a fragment of Zero bearing a sample of his DNA. With the assistance of another Reploid scientist named Isoc, he was able to almost completely decrypt Zero's code, but the viral sample caused him to go Maverick in the process. This led to him not only resurrecting eight of his creations but also creating a new Reploid named High Max and a crazed copy of Zero, dubbed the Zero Nightmare, all in the name of establishing a world for Reploids that he could rule over.

From behind the scenes, Gate had Isoc carry out a series of Maverick attacks, laying the blame at the feet of the Zero Nightmare. Gate's creations were dispatched as "Nightmare Investigators" to allegedly get to the bottom of the incidents while inciting further discord.

SPOILER: Maverick Hunter X was dispatched to investigate the Zero Nightmare himself and, along the way, discovered that the real Zero had returned. Together, they retired the resurrected Investigators as well as High Max and rescued the other Reploids who'd attempted to help. The Hunters would confront Gate in his secret lab beneath the Eurasia crash site. Using the data he'd gathered, Gate created battle armor for himself that would prove impervious to all attempted attacks, yet was vulnerable to his own Nightmare Holes.

The Nightmare Holes were energy projectiles with varying effects based on color: red slowed an opponent's movements, while orange fired further projectiles, blue drew opponents in, green started to slowly home in on targets after being fired, and purple created Nightmare Viruses. The projectiles were volatile, however, and dispersed in a scattershot manner when attacked, which was used to bring Gate down.
In addition, Gate attempted to knock the Hunters from their precarious footing by ramming them with his Nightmare Move, and used tall but narrow Nightmare Strikes to destroy the footholds scattered around his arena.

Though defeated, Gate's end came not at the Hunters' hands but those of Sigma, whom he had been in the process of reviving. X later returned to Gate's lab and retrieved his body for the sake of one of his colleagues, Maverick Hunter Chief Navigator Alia.