In 1963, Murray Gell-Mann (a scientist) suggested that there were particles inside the protons and neutrons that make up the nucleus of an atom. He said that the behavior of these subatomic particles could be explained by the existence of a particle with three parts. He had read "Finnegans Wake" by James Joyce and saw the phrase "Three quarks for Muster Mark" and thought about how there are three quarks inside a proton.
Photo courtesy of AIP Emilio Segre Visual Archives.