This is Dr. Jean Laszlo, I'm still working out their exact timeline and stuff, but here are his main lore details:

He was a research assistant at the Umbrella corp. while working on a PhD. in gene editing, using geckos as a study species.

Basically they were trying to make super geckos that could regenerate more than just their tails, hoping to eventually try transferring those traits to humans.

So naturally they got bit by one of the mutated zombie geckos on accident (or maybe infected himself on purpose? haven't decided yet) and started slowly transforming into a big gecko monster, because it's resident evil and i'm a furry lol

When Gideon bought the Rhodes Center after Umbrella collapsed he invited Jean to come work for him there as a researcher. They were in a weird sort of situationship back in the Umbrella era, fell out of touch for a bit after the whole Raccoon City went down, then got a lot more involved once they started working together again.

Jean's also about 8 years younger than Gideon, because that's about as far as I could resonably push an age gap and still have it make sense with the timeline

Also his mutated design is based on a white morph gargoyle gecko