Dr. Weil

"The desire for power. The joy of making everything work for you. You have no way of experiencing this without a human brain. It's the ultimate joy! No mere Reploid could ever understand!"

- Dr. Weil "Humans are like pigs, dependent upon the Reploids for their very existence...You do realize, don't you, that if I felt like it, I could wipe all humans out in the blink of an eye? Crea! Prea! Do with this one as you please! I've got some pig squeals to enjoy. The squeals of indolent pigs, wasting their pitiful lives on idle pursuits."

- Dr. Weil "I am the Devil!"

- Dr. Weil

Dr. Weil is the main antagonist of the Megaman Zero franchise. He is the one responsible for the Elf Wars, which caused a mass genocide for both humans and Reploids. Returning from his exile, he takes revenge and becomes the new ruler of Neo Arcadia.

Before Megaman Zero
During the Maverick Wars, Dr. Weil was one of the researchers that were studying a way to definitely destroy the Sigma Virus, who caused reploids to turn into mavericks. Zero discovered that his own body was spreading the virus, so he offered his body to the researchers. His memory data was transferred to a new body. It was then that Weil studied his body, discovering that Zero was created to be a bloodthirsty war machine. Weil, along with another researcher, created the Mother Elf, who was able to counter the Sigma Virus and completely destroying it, thus ending the Maverick Wars.

However, Weil become very unsatisfied with the result of the war, as he thought the reploids should pay for all the destruction they caused to Earth. Weil then cursed the Mother Elf by putting the Sigma Virus data into her, turning her into the Dark Elf. Next, Weil took the original Zero's body and modified it, thus creating Omega, who could absorb the Dark Elf to maximize his own power. Using Omega, Weil was able to take control over most reploids in the world, thus starting the Elf Wars, which wiped out 60% of the reploids and 80% of the humans in the world, creating a great wasteland. X, along with Zero, managed to defeat Omega in a combined attack. Omega was sent into space to never return, and Weil was condemned to being put in a mechanical body who would regenerate his cells, making him immortal, and then banished into the same wastelands he created, cursed to suffer forever and remembering what he did. X used his own body to seal the Dark Elf in the core of Neo Arcadia.

During Megaman Zero
After Elpizo destroy X's body, releasing the Dark Elf, Weil sees the perfect opportunity to return and start his plan to take his revenge. The ship where Omega was imprisoned falls on Earth, and as Zero and the Neo Arcadia guardians goes to investigate, they are confronted by Omega. Weil appears shortly after, with a reconstructed Copy X, who claim his place as ruler of Neo Arcadia. Copy X assigns Weil as his advisor, and both Neo Arcadians and Zero start a rush after the Dark Elf. Weil then orders a large rocket over a residential area, where the Dark Elf is, with Omega on board. As the rocket crashes, Omega absorbs the Dark Elf, now reaching full power. Later, Zero confronts and defeat Copy X, but as he tries to power up, he explodes.

Weil waited for this all along. When he reconstructed Copy X, he set up a bomb on him. Weil then called for the law, assuming the rule of Neo Arcadia. Although Zero destroyed Omega, Weil now had everything he wanted. He ruled over Neo Arcadia with iron fists, and anyone who opposed him were labeled maverick, being reploid or human, and were ordered to death. As some people started to flee from Neo Arcadia, he started the Ragnarok project, in order to destroy everything outside Neo Arcadia, so nobody would have delusions of escaping his rule.

As many humans fled from Neo Arcadia and made a settlement in Area Zero, the area where the space colony Eurasia had fallen in the distant past, Zero had to fight Weil's forces and protect the humans. Zero made his way into the Ragnarok, where he fought Kraft, who had assumed control of the satellite, firing it on Neo Arcadia, completely destroying it. After defeating Kraft, Zero was forced to take an alternate route to reach the core of the Ragnarok, where he found Weil. Weil fused himself with the core, forcing Zero to fight him. He was defeated, but used his last strength to fuse with the entire Ragnarok, sending it to crash against Earth. Zero fought him again, destroying Weil and the Ragnarok, but dying in the proccess.

Personality
Weil is malevolent, ruthless, and cruel individual who will do anything to achieve his goals. Sacrificing others is never a problem for him.