Broly
Unfortunately Broly doesn't show up until the late part of the GT series. His origin is still mysterious since Vegeta, Nappa, and Goku were supposed to be the only survivors of the destruction of the planet Vegeta. However, many speculate that Broly is the legendary super saiyan that mysteriously disappeared a long time ago. It is also said that as a child, Broly was in a crib next to Goku, but Goku's constant cying bothered Broly and that is why he set out...to train and be better than him. It is rumored that Broly is so powerful that when he turns super saiyan, his power level only increases by 2,000.