What is an electron made of? And don't reply that it is an elementary particle or a string.
So what kind of reply do you expect?
Welcome to PhysicsForums, David!
Electrons are considered fundamental particles without an underlying structure. They have charge, spin, rest mass, and a few other things. You can check wiki for the basics. Is there something more specific you are looking to understand? Quantum particles (such as electrons) do not necessarily resemble objects in the classical world.
"What is 2+2? And don't reply that it is 4...."
As far we know (and we've been working on this for better than a century now) an electron is an elementary particle, meaning that it has no internal structure and it's not made of anything. There are interactions that create new electrons, and there are interactions that destroy electrons, but there are no interactions that break an electron into smaller pieces that you could say it is "made of".
Even if we did find something that electrons were made of, sort of like how protons and neutrons are made of quarks, that would just push the problem down one level - we'd ask what that new something is made of, and we would rinse and repeat forever. Sooner or later we're going to come to some basic building blocks that cannot be further subdivided, and all available experimentation and theory says that the electron is one of them.
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