Tetraethyllead

Tetraethyllead is like a bad guy that used to be in gasoline to make cars go vroom vroom. But, like all bad guys, it was very mean and was hurting the Earth and people. So, the people who make rules said "no more tetraethyllead in gasoline" and now cars use something else to make them go vroom vroom without hurting the Earth or people. So, now we can all be happy and breathe clean air without that bad guy around.