If we set aside Hollywood for a moment to talk about something unexpected... this is a completely serious and rather interesting subject of study:

https://en.wikipedia.org/wiki/Philosophical_zombie

My position on the matter is that it is quite easy to design systems that are to some degree "intelligent" (for most definitions of intelligence), without possessing qualia (consciousness, subjective experience). Several such systems exist, and you have probably heard of them!

Moreover, I think many natural persons can be intelligent without being conscious, at least sometimes. I think many people have this experience when working on difficult problems, e.g. programming.

For Hollywood-style zombies? I would start with chemistry rather than biology. There are many substances that can alter our mood, body control, aggression, and consciousness. Find a mix that creates the effect you want, and create an implant (or make it an addictive drug mixture). Probably the result would be less consistent than hollywood-style zombies. It would not be contagious though.

Or if sci-fi, insert genes into a living person that encodes a system to internally synthesize the drug mix.

Edit: Something that makes most people into shuffling drones? Increases aggression? Spreads like a disease? A cynical answer would be that we have invented that already. We call it "capital".