There was a period of time in Grand Prix motorcycle racing (The 80s and early 90s) when Australian and American riders were absolutely dominant. Both countries had thriving off-road and dirt-track racing communities, while European and Asian countries did not. As the Grand Prix motorcycles became more and more powerful, riders that could slide the machines turned out to be fastest around the track.
Kenny Roberts was the prototype dirt-track rider who become a successful Grand Prix rider, and he was in turn followed by many others. The bikes were as amazing as the riders. They were powered by very light two-stroke V-4 engines that were pushing 200 very peaky horsepower.
The tires of the day weren't really up to the task of maintaining grip consistently. And unlike today, there were no sophisticated electronics to cut engine power in turns or for launching. A heroic time really.
The videos below capture a sense of how vicious these powerful motorcycles were, and how awesome the guys were who rode them at (and over) their limits.