What subatomic particle has the least mass?

An electron has the least mass of any subatomic particle, with a mass of 9.1 x 10^-31 kilograms per electron. Electrons are found in the electron cloud, an area that surrounds the nucleus of an atom.

Electrons hold a negative charge equal to the positive charge found in protons of the nucleus. They generate an electric field, exerting an attraction towards particles with positive charge such as protons or a repulsion against particles with negative charge. When electrons are in motion, they generate a magnetic field. Sir John Joseph Thompson discovered the existence of electrons in 1896 through experiments involving cathode rays.