Broli is the profecised Legendary Super Sayain that comes every one thousand years. He has hated Goku from the time that he was born. Goku and Broli were born at the same time and when Goku was born he was crying and he woke Broli up and has held a grudge ever since. When Goku was born his power level was 10 and when Broli was born his power level was already at 10,000.