What Are Quarks?

In the 60s and 70s, scientists started putting forth the idea of quarks. Barions are a subtype of hadrons where there are only three quarks present in this particle. What is anti-matter? If you can search up really quickly, like how anti-matter was discovered, that would be really cool because I don't know how it was discovered or theorized. Maybe they just thought of it as again, the similar thing to the positron antimatter.