Quark
The quark model was independently proposed by physicists Murray Gell-Mann and George Zweig in 1964. Quarks were introduced as parts of an ordering scheme for hadrons, and there was little evidence for their physical existence until deep inelastic scattering experiments at the Stanford Linear Accelerator Center in 1968. Accelerator experiments have provided evidence for all six flavors. The top quark, first observed at Fermilab in 1995, was the last to be discovered.
Kazuhiko Nishijima
where "Q" is the electric charge, "I" is the isospin projection, "B" is the baryon number, and "S" is the strangeness quantum number of the particle. This formula was pivotal for the later development of the quark model by Gell-Mann and George Zweig in 1964 (independently of each other).