The electron was discrovered by J. J. Thomson.
It was discovered during an experiment where Thomson was probing the properties of cathod rays which were produced when high electrical voltage was applied between two electrodes with a cathode ray tube.
He noticed a stream of particles, which came to be known as electrons.
Electrons are negatively charged, and were independent of the material from which they originated. The charge to mass ratio of the electron is -1.76*10^8 C/g