Top quarks are the heaviest fundamental particles we’ve found so far. By fundamental I mean that there’s nothing else inside, you can’t break it apart. Top quarks weigh about the same as a gold atom. Gold atoms are themselves made of 79 protons, 79 electrons and about 118 neutrons. Protons and neutrons themselves contain 3 quarks each (different quarks to top quarks though).
What’s cool about the top quark is that we can study it “naked”. Since a top quark is so heavy, it doesn’t live very long, like a really fat cat. A top quark lives for such a short time that it doesn’t dress itself with other particles, or never covers itself up with other particles as clothes. The lifetime of a top quark is about 0.00000000000000000000000005s (25 zeroes!). If you blew this time up to 1 second, and blew up the 1 second by the same amount, the 1 second would be about 5 million times the age of the universe!