Siegfried Von Schroider's family has a long feud with Kaiba's, which started when they were kids, as Siegfried's father's business partner Gozaburo Kaiba kept stealing business deals under his nose, leading to his premature retirement. When Siegfried took over the family business and decided to turn his company into the gaming business, he discovered that Kaiba did so with his own years prior, unintenionally robbing him of business opportunities. Finally, Siegfried chose to work on a device able to project Duel Monster cards, only to to find out that Kaiba came up with a better one, finally making him snap.
Grand Championship Tournament
As revenge, Siegfried attempted to sabotage Kaiba's Grand Championship at Kaiba Corp. First, he set a computer to trap everyone inside, but the computer was defeated by Yugi Muto. Siegfried entered the tournament as Sieg Lloyd, and easily defeated Insector Haga and Dinosaur Ryuzaki using his Valkyries Cards. He then dueled Katsuya Jonouchi and won.
As he was about to face his younger brother Leonhart in the final round, Kaiba realized his true identity and dueled him. Kaiba won, but Siegfried still had his main plan up his sleeve while Leonhart was dueling Yugi in the finals, Siegfried had him play a card called the Golden Castle of Stromberg, which was infected with a virus that deleted Kaiba's data. Leonhart, who had no desire to willingly participate in evil plans, and Yugi were able to stop it during their duel. After Yugi defeated Leon, Kaiba revealed that all his information was saved on a backup, and was never lost. Siegfried was utterly defeated, and Leonhart convinced him to make his corporation as good as Kaiba's without doing anything evil.