The ability to become a Super Saiyan was once considered to be nothing but a legend, because it had not been performed for over one-thousand years (three-thousand in the Ocean dub). Vegeta stated that a Super Saiyan has achieved a level of power so overwhelming that it could only be maintained in a transformed state. Despite only being told through legend, Frieza (who was considered to be the strongest being of his time) became paranoid over the possibility of truth behind the legend of the Super Saiyan because of the constantly growing power of the Saiyan race. Because of this fear, Frieza drew the conclusion to annihilate the Saiyan race by destroying Planet Vegeta (with nearly every Saiyan), thus sparking the end of the Super Saiyan legend. Over two decades later, this legend was proven to be true when Goku accomplished the feat while maintaining this state in his original form during his titanic battle against the evil tyrant, Frieza.The depiction of the original Super Saiyan that appears in Vegeta's telling The Super Saiyan transformation comes in response to a need, not a desire. In all known cases, the form has been initially triggered by either desperation or indignation. Any other conditions are unknown, and motivation tends to differ; for example, Goku achieves the form out of anger over the murder of his best-friend Krillin, while Vegeta achieves the form through sheer frustration at his original inability to achieve it especially over Goku. While training in the Hyperbolic Time Chamber, Goku tells Gohan that becoming a Super Saiyan is powered by rage and told him to imagine Cell and then Frieza when Gohan said he had never seen Cell, killing all his friends to transform into a Super Saiyan. Saiyan hybrids are naturally skilled at this, as they have the emotion of Humans (full blooded Saiyans tend to suppress their feelings) with the fighting potential of Saiyans. As the Saiyans train during Dragon Ball Z, they discover uncharted levels beyond the first Super Saiyan level. The power increases of subsequent Super Saiyan forms are so high that by the Buu Saga, the original transformation has been literally reduced to that of a "child's play thing" (as stated by Vegeta; as both Goten and Trunks can transform and harness the power adeptly at such a young age).
In the main series, all living Saiyan-blooded males after the Frieza Saga manage to reach at least the first level of Super Saiyan. No female Super Saiyans are ever seen in the anime/manga. However, the Dragon Ball GT Perfect Files implies that Pan has the potential to transform and might have become a type of Super Saiyan never seen before.