The government, but I don’t think the line between the bourgeoisie and the proletariat is that clean. I think the definitions of these classes is pretty fuzzy.

I think you underestimate the number of people who want power, and the variety of reasons someone might want to be an oppressor (wealth, control, security, status, fame, respect, not to mention people who think they’re doing the right thing). It only takes a handful of people anyway, and those are exactly the types of people that would be drawn toward working in the government so that they can oppress the remaining capitalists.

Even if you managed to make the kind of classless society you’re talking about I suspect that oppressive systems would grow out of it. Think of something like an HOA, people trying to control others “for the good of the community”. Without an authority structure above it, I suspect it would grow and bloat, granting itself more power and authority as time went on. Eventually you’ve got a new oppressive government explicitly built by people who want to control others.

Getting that from an HOA might be ridiculous, but HOAs demonstrate the desire for control I think is all too common.