Gozaburo Kaiba

Gozaburo was the original founder and CEO of Kaiba Corporation, which at that time was a successful arms manufacturer.

He was also a world famous chess champion, which is how Seto and Mokuba heard of him at their orphanage. When Gozaburo visited, Seto challenged him to a game of chess, telling Gozaburo that if he refused, he would tell the press he was scared of a little kid. Gozaburo, confident he would not be beaten by a child, agreed to a single game, with Seto stating the stipulation that if he wins, Gozaburo will agree to adopt him and his brother. In the manga, Seto cheated. In the anime, Seto had spent time studying Gozaburo's strategies and how to overcome them, and thus defeated him.

Gozaburo had to keep his end of the bargain.

However, he was a cruel father to Seto, forcing him to spend all his time studying and forgoing any of the joy or fun usually associated with childhood. At this point his biological son Noah died as well. With his intended Kaiba Corp heir digitized, Gozaburo decided to breed Seto as his heir, pushing him even further.

It is revealed that Gozaburo instead digitized his mind like he did his son's, and hid inside the Kaiba Corp computer banks. When Noah lures Seto and others, including Yugi Muto, into the Virtual World, Gozaburo has Noah and the Big Five try and defeat Seto and company. When they fail one by one, Gozaburo reveals himself as the mastermind of the capture, and unveils his plan to digitize mankind, and rein as the king of the Virtual World (this is in the English anime: the Japanese Gozaburo plans to use missiles to destroy the world)..