Gary Oak is a Pokemon Trainer and the rival of Ash. He is the grandson of Professor Oak. He and his sister Daisy lost their parents in the same accident as Ash's father. From then on, their grandfather took care of them. He wasn't bery good at raising children, and he always gave them what they wanted. Gary grew to be a very arrogant and selfish boy. On the contrary, his sister was a lot more modest. She knew of her talents, but she didn't boast as much.
In Elementary School, Gary became the most popular boy in school by bullying the other kids and being feared by them. His classmates saw him as invincable. Ash was his main target, bullying him for the loss if his father. When Ash knew about Gary's parents, he spread the story through school. Gary has hated him ever since.
At the age of 10, he also got into the Viridian Trainer Academy.
When he heard the news about Ash getting his Starter at an early age, he demanded to get his one too. Professor Oak conceded, and gave him an Eevee, imported from Johto.
Gary's plan was to always be one step ahead of Ash, so he competed in the Pokemon League. But he finds out that always being faster than Ash has its consequences...