List of Grand Prix motorcycle racing World Riders' Champions
Grand Prix motorcycle racing is the premier championship of motorcycle road racing, which has been divided into three classes: MotoGP, Moto2, and Moto3. Former classes that have been discontinued include 350cc, 250cc, 125cc, 50cc/80cc, MotoE, and Sidecar.
Source: Wikipedia — List of Grand Prix motorcycle racing World Riders' Champions (CC BY-SA 4.0)