Legendary Super Saiyan
The Saiyan legend was passed down by almost every Saiyan family. This legend spoke of a great myth. This myth stated that every millenia a Super Saiyan would emerge. These Saiyans would have extreme power, and much different characteristics. It also stated that no one in the entire galaxy could defeat the one who possesses this power.
As for the Legendary Super Saiyan, well I have this to say. Brolli is not the real Legendary Super Saiyan. Brolli was born a Super Saiya-Jin, he never really turned it. Yes he was indeed the first Super Saiyan, but being born a Super Saiyan, is not turning it. As the real Saiyan legend clearing states: Every Millenia a Saiyan would turn to this extreme form. However, the legendary SSJ is supposedly Goku, but I am still not 100% sure of that.