The charge of an electron being negative is a fundamental property of the electron in the framework of our current understanding of physics. In the standard model of particle physics, which describes the fundamental particles and their interactions, electrons are classified as elementary particles with a specific charge value.
The origin of the negative charge of an electron is not fully understood at a deeper level. In the standard model, elementary particles are considered to be point-like entities without any internal structure. They possess certain properties, such as mass, charge, and spin, which are intrinsic to them.
In terms of electric charge, there are two types of charges: positive and negative. The proton, which is one of the building blocks of atomic nuclei, possesses a positive charge. On the other hand, the electron carries a negative charge, which is equal in magnitude but opposite in sign to the positive charge of the proton.
One way to think about the negative charge of an electron is that it arises due to a fundamental property that distinguishes it from particles with positive charge. This property is often referred to as "electric charge" and is a conserved quantity in various physical interactions.
While we know the behavior and properties of electrons with negative charge through experimental observations and theoretical models, the underlying reasons for why electrons have the charge they do are still a subject of ongoing scientific research.