Kaiba Noa was the son of Gosaburo, the wealthy owner of Kaiba Corporation. He was extremely intelligent, and, being a "privileged child," he was able to participate in many activities, including sports. His life was, basically, perfect.

Then, tragedy struck. One day, as he was outside, a car came hurling out of nowhere and hit him. He was immediately sent to the hospital, but despite Gosaburo's constant badgering of the doctors, Noa passed away.

Noa then was put into a simulated reality by his father, so he can still hopefully one day take over the company, although when Gosaburo decides this is impossible he adopts seto and mokuba and forgets about Noa, this makes Noa very angry and in season 3-4 he decides to capture Seto and Yugi and put them into his simulated reality world, if he wins he gets one of their bodies so he can live in the real world and take over the company.

(Source: Tiny Tenshi)