Till date, there have been many subatomic particles discovered by scientists. Still, the discovery of electrons is regarded to be an important chapter in the history of subatomic particle research.
Even now, when we're aware of nearly 70 or more parts of an atom, the discovery of electron, proton, and neutron; the most important atomic components, is said to have laid down the foundation stone for further research in related studies.
Johann Wilhelm Hittorf
In 1869, a German physicist, John Wilhelm through his extensive research on electrical conductivity in gas tubes discovered that a glow emitted from the cathode plate in the experiments he conduced, and the intensity of the glow is dependent on gas pressure.
In 1876, this German physicist was able to find that the rays emitted from the glow in the earlier experiment carried out by John Wilhelm cast a shadow, if an object is place behind it. He named them as cathode rays.
In the 1870s, the English Physicist and Chemist, William Crookes constructed the first cathode ray tube that led to the development of the theory that negatively charged particles are present in the rays that get deflected from anode to cathode.
This German-born British physicist worked intensely on Crooke's work, and it was now almost sure that these rays carried some negatively charged particles. However, Crooke's calculated charge to mass ratio (e/m) was way higher than expected, so his results in 1890 weren't given much weightage.
Now that the scientific community was aware of the fact that the cathode rays contained some negatively charged particles, the result was finally established by a team of British physicists.
Sir J. J Thompson: The Man Behind Electron's Discovery
It was in 1896, that the British Physicist, J.J Thompson and his colleagues named John S. Townsend and H. A. Wilson performed several experiments and conclusively proved the existence of electrons.
Through his experiments, in which he used Cathode ray tubes, Thompson established that these rays were particles unlike waves, atoms, or molecules. He also calculated the approximate value of 'e' (electronic charge) and 'm' (mass ratio). He however, could not calculate the value of charge and mass of the electron independently.
This came to be known as the Millikan Oil Drop Experiment, and it is said to have given an exact measure of the electronic charge. For his valuable contribution in the discovery of electron and on his work on conduction of gases, Sir J. J Thompson was awarded the Nobel Prize in 1896.
Later, De Broglie and Albert Einstein did phenomenal work in establishing the wave and particle nature of electrons.