Are you curious to know why Brolly is just so cool? Then read on!!!

Brolly was born with a power level over 10,000, and because of this was considered a threat by the King Vegeta, who thought the baby Saiyan would grow up to be more powerful than his son, which he was and would be throughout his life. Before he was supposudly assassinated, along with his father, he developed his hatred for Goku, which developed when they were both babys. This is because he (Goku) was crying so loud and so much that it forced Brolly to cry, and apparently he did not like that one bit. So now Brolly hates Goku and would forever remember him and want him destroyed, though he wouldn't realize it until he met up with him years later. After their 'assassination,' Paragas (Brolly's father)and Brolly were thrown away like trash. When the planet Vegea was soon destroyed after that, Brolly sort of 'woke' up and went on a berzerk crying spree of sorts, grabbed his father, and left the planet as it was annihilated by Frieza, protecting he and his father with his incredible power. They traveled through the universe with Brolly destroying almost everything he could get his hands on. Eventually, Paragas got a scientist to create a device with which he could control Brolly (the thing that looks like a gond headband), and, in his hopes, take over the universe...

Well, I don't want to give it all away. If you want to see the full story, then you should watch DBZ movies 8, 10, and 11 (I know, they didn't come out in english here yet, but if you're really a Brolly fan, subtitled will have to do^_^)