yu-gi-oh! (toei)
A 1998 anime and the first adaptation of the Yu-Gi-Oh! manga series by Takahashi Kazuki, produced by Toei Animation. It adapts the first 59 chapters of the manga in a heavily abridged format, and is popularly known as Season Zero by fans.
The series tells the story of Mutou Yuugi, who after solving the ancient Millennium Puzzle, awakens a gambling alter-ego within his body that solves his conflicts using various shadow games.
The anime also had a theatrical movie released in 1999, which focused on Aoyama Shougo gaining the legendary Red-Eyes Black Dragon as he learns to bring out his confidence to duel.
It's succeeded by Yu-Gi-Oh! Duel Monsters.