One of the most hotly debated subjects in all of Mega Man history is the connection between the classic series and the X franchise. It's mostly known that Dr. Wily created Zero in the image of Proto Man, and some speculate that he proceeded to run amok and kill everyone in the classic series off -- explaining their absence in Mega Man X.
The former confirmed factoid is explicitly stated and shown in the arcade fighter Rockman: The Power Battle, as well as the sequel, The Power Fighters, and the more-canon anime cutscenes in Mega Man X4. Thankfully, this new design document that's on display at the Mega Man 30th anniversary event in Hirakata and Hanayashiki Park Japan gives us a few more clues.
Staggeringly this document dates back to 1993, before Bass, Wily's big project, was ever a thing (Mega Man 7 didn't come out until 1995). It details the creation of both X and Zero by Dr. Light and Wily respectively, as well as the creation of the robot virus by Wily, which led to the Maverick virus that shook up the entire world in the X series. Another big thing to notice -- Dr. Wily died "at the same time" as he completed Zero, and his virus, which was incomplete, assisted in turning Zero to the good side.
As silly as this subseries got over time, it's amazing to see how planned out it was from the very start.
N2 [Twitter via Rockman Corner]
via destructoid https://www.destructoid.com/mega-man-x-design-document-further-explains-the-zero-and-dr-wily-connection-487385.phtml