The identity of the electron goes back to 1752 when Benjamin Franklin's discovery set other scientists out trying to see if electrical energy could travel through gases other than the atmosphere. This was proven to be true and that electrical energy and particle movement also produced a ray even when it was not moving through any gas. This surprised early investigators because they thought the ray was associated with the gas instead of an entity in and of itself! Tests also showed that the ray was blocked from reaching the Anode (+ charged end) when something was in its path. So they reasoned the ray originated from the Cathode (- charged end) and named it a cathode ray. The experiments where therefore done in a cathode ray tube.
Further experimentation proved that magnetic fields could deflect a cathode ray. The speed of of this ray was found to be much slower than the speed of light. This characteristic was more indicative of a beam of particles as opposed to a beam of light. .
In 1897 Thomas measured the deflection angles of cathode ray particles in a magnetic field. His formula, angle of deflection = charge/mass furthered the idea that the cathode ray was made of particles, because his formula basically says the greater a particle's mass is the greater its resistance to a change in motion. This wouldn't happen if there weren't particles! In 1909 American physist Millikan calculated the numerical value of a single increment of electrical charge. He proposed that the coulomb to be the fundamental increment of all electrical charge. Using this value and the charge to amss ratio discovered by Thomas, millikan calculated that the mass of a cathode ray particle was smaller than the smallest known atom, hydrogen.
We now know that the cathode ray particle is an electron, and a cathode ray is a stream of electrons.