What do we know, and what don't we know about the electron?
We know a great deal about electrons. For all
practical purposes, we know everything there is
to know about electrons.
What an electron "is" can be stated in terms of
its mass, charge, spin, and lepton number.
What an electron "does" is described by gravitation
and quantum electroweak dynamics.
Some guy named Feynman wrote a book _QED_ that
covers this with breadth and a good bit of depth,
demanding little of the reader by way of scientific
background (less than high-school physics).