1964 Murray Gell-Mann & George Zweig
Murray Gell- Mann was an American physicist who received a Nobel Prize for his theory on elementary particles. He also found that all the elements of an atom are held together by quarks. To find this, he blasted high speed electrons into a hydrogen atom.
George Zweig proposed the existence of quarks. He thought of them as aces, because he guessed there were four quarks in every atom.
Now, in the same year, both these guys proposed the idea of quarks. They tested electrical charges, and that how the numbers for quarks came about.