In particle physics, an elementary particle is a fundamental subatomic particle that cannot be broken down into smaller components. The Standard Model currently recognizes 17 distinct types, including 12 fermions (like electrons and quarks) and 5 bosons (force carriers), which account for 61 known variations. This distinguishes them from composite particles such as protons and neutrons, which are made of quarks.
Historically, atoms were thought to be indivisible until Albert Einstein's 1905 work confirmed their existence, followed by the discovery of particles like the electron, proton, and neutron by 1932, revolutionizing our understanding through quantum mechanics. While incredibly successful, the Standard Model has limitations, notably omitting gravity, and theoretical elaborations like supersymmetry propose undiscovered "shadow" partners, remaining a key area of research. Ultimately, the visible mass of the universe is predominantly composed of protons and neutrons, which are themselves made of up and down quarks.