The Saiyan race are an identical aliengena humans but much more advanced and only differs in one thing. They possess a power capable of using the energy of their bodies to fight, this makes much msrpidos and resilient.
In addition this energy can be used for many things like fly, cast rays, hitting with more power and many more. This makes them a people super warriors battling across the galaxy to measure their skills and dominate the space, but his lust for power is also its greatest weakness as just finding enemies that can not exceed and fall in combat .
Now there are few of these warriors, since their home planet was destroyed and only some of them have survived. In addition they are scattered across the galaxy, but they are aware or not they are part of this great people have a tremendous aptitude for combat.
Some of these warriors utilizarn these skills for good and Goku and others dejarn lead astray in an evil convirtindose able to whip the world.