Gate

Gate (ゲイト, Geito) is a Reploid Scientist and main antragonist of Mega Man X6. He used to be a colleaque of Alia. His goal is to create the ultimate Reploid and a new world order for surpreme Reploids only and is completely devoted to his work in order to achieve what he desires the most. Gate is the creator of the eight Nightmare Investigators, the Zero Nightmare, High-Max, the Nightmare Virus itself and is partially responsible for the resurrection of Sigma.

Personality
Gate is a devoted researcher with a cold and sarcastic attitute. In order to achieve his goals, he's willing to do everything necessary to get what he wants. He became bitter and filled of hatred when his creations were destroyed by his very own colleagues, especially because Alia (who's often speculated to have helt romantic feelings for him) was part of the conspiracy.

Researcher days
Gate used to work in a team of Reploid scientists, researching the potential of Reploid engineering. He was fascinated by the Maverick Hunters X and Zero because their body structures and DNA was a mystery to the world's finest scientist and researchers. Both of them were completely non analyzable and their inner functions couldn't be fully understood. He saw it as a challenge to find a way of analyzing both of them or at least creating Reploids with similiar attributes. Eventually, he suceeded and created eight Reploids whose DNA couldn't be analzyed by the other scientists, Commander Yammark, Rainy Turtloid, Shield Sheldon, Blizzard Wolfang, Blaze Heatnix, Infinity Mijinion, Metal Shark Player and Ground Scaravich. Gate's Reploids were widely praised and used in various locations for several duties. However, this casted the jealousy of his colleagues upon him and they eventually began conspiring against him and his creations, Alia was one of them. All eight of his Reploids were either trapped while on duty or labelled Maverick, but in any case, all of them were destroyed. Broken and bitter, Gate left the research team, becoming an ananchorite somewhere on Earth. However, things changed when the remains of the Eurasia crashed near his refuge...

Mega Man X6
Two weeks after the Eurasia incident, Gate visited the the crashsite. There, he found something. At first, he thought he had merely found a piece of junk but it soon proved to be something far more powerful. It was a piece of Zero, more importantly, a DNA sample of Zero. He immediately began analyzing it and after roughly a week of study, he had been turned insane by Zero's viral DNA, however, he called it a very "liberating" experience. With the help of the mysterious Reploid Isoc, he managed to decrypt 99,98% of Zero's DNA, creating the Nightmare Virus from it, as well as the powerful Reploid High-Max and resurrecting his eight dead creations.

Both of them then came up with a plan to use Zero as a scapegoat for creating a new society of Reploids, selected, powerful Reploids, independent from humanity, the ideal state, lead by Gate. To do this, he created a purple, apparently insane copy of Zero, called the Zero Nightmare which was then publically blamed for the recent Maverick attacks by Isoc. Isoc offered Reploids all over the planet to join the Nightmare Investigators to hunt down and destroy the Zero Nightmare to bring back peace.

Eventually, Gate would contact the Maverick Hunters upon their victory over his creations or a temporal defeat of High-Max, inviting X and Zero (if found by X after the destruction of the Zero Nightmare) to challenge him. He later revealed to X/Zero that he didn't set up all this on his own, but with the help of Zero's DNA. In order to gather and analyze even more data about the two ancient robots, Gate challenged X/Zero in battle, using all the data he had analyzed by now, using a golden battle armor that made him virtually invincible against attacks, except if his own attacks were repelled against him. X/Zero managed to find this weakness, and defeated him, leaving him behind damaged and unable to move. Gate however, refused to give up. Although he didn't want to do it, he unleashed his final trump card: a revived (yet completely insane) Sigma. Unfortunately for him however, Sigma refused to acknowledge Gate's part in his resurrection, nor needing him for anything, blasting him.

After Sigma had been defeated, X returned to the remains of Gate's laboratory, salvaging his body because he was unable to leave him there as he used to be Alia's friend. Yet, he had been damaged beyond repair. Alia was given the choice what to do with Gate, repairing him or else, however it never was made clear and his fate remained unknown.

Trivia

 * Although Gate's battle armor never received an official name, it was dubbed "Zero Armor" by fans because many believe it was created from Zero's DNA like most of Gate's creations.
 * The theme of Gate's laboratory is a remix of the third X-Hunter stage from Mega Man X2.