Brolly, he was born on the saiyan homeworld with Goku. Their cribs were placed next to each other. While Brolly was born with a power level of 10,000 and Goku had a meager power level of 2. When they were babies Goku managed to make Brolly sad and cry with Goku's persistent whining that wouldn't stop. This is what drove Brolly's anger towards Goku, Goten, any other dbz warrior and his love of being evil.
While Brolly was a baby, King Vegeta learned of this child of Paragus that was born with amazing power for a child. King Vegeta had both Paragus and Brolly "thrown away" like trash. When Freeza destroyed the planet, Brolly used his amazing power to protect both himself and Paragus from the destruction.
During Brolly's childhood Brolly became increasingly difficult to control, Brolly's power was greater than ever imagined. Paragus had a scientist from a world he conquered create a device to control Brolly, similar to a remote control of sorts. When Paragus essentially had this great power at his control, he created a "New Planet Vegeta" in an attempt to draw the Saiyan Prince(Vegeta) to the new world where Paragus would have his revenge on King Vegeta by killing his son Vegeta by either the comet that was heading towards the new planet or by Brolly himself. The plan did not work completely as planned and Paragus told Vegeta of the Legendary Super Saiyan who was near the new world that was destroying entire galaxies. This is what made Vegeta go to the new world.
The rest of Paragus's plan seemed to be working accordingly, but the arrival of Goku at the new world shortly after Vegeta caused problems. Seeing Goku, drove Brolly's anger and eventually Brolly could not be controlled by Paragus 's device and his plan was revealed to the saiyans. Paragus tried to escape from the planet before it's eminent destruction but Brolly destroyed his space pod, with Paragus in it, killing him.
Through a very long and rigorous fight, Goku did finally defeat Brolly in movie 8 with the help of the others (Piccolo, Gohan, Trunks, and Vegeta). Brolly returns and somehow he survived Goku's deathblow and managed to get to another space pod, this space pod lands on earth. There is another battle, Goten and Gohan use a large Kame hame ha to defeat Brolly. At first there is no effect but Goku's spirit falls from the clouds and gives them emotional support as well as joining in on the Kame hame ha which does destroy Brolly. Finally he returns one last time, he is cloned and is once again destroyed by Chibi (young non-future) Trunks and Goten.
