Yu-Gi-Oh! "King of Games", occasionally subtitled "A Game of Darkness", "First Season", or "Season Zero" by fans) is the first anime adaptation of the Yu-Gi-Oh! manga series. The 27-episode series was produced by Toei Animation and aired on TV Asahi from April 4 to October 10, 1998.
While this series is not directly connected to Yu-Gi-Oh! Duel Monsters (known internationally simply as Yu-Gi-Oh!, produced by Nihon Ad Systems and aired on TV Tokyo), both anime series are based on the Yu-Gi-Oh! manga.
Manga plots were re-written so that they could take up an entire episode's worth of time. Also, the level of violence was reduced between the manga and the anime. Finally, a minor character in the manga, Miho Nosaka, became a main character in the first series along with Yuugi Mutou, Katsuya Jounouchi, Anzu Mazaki, and Hiroto Honda. Characterization was slightly modified. For instance, Miho is a "ditz" in the anime while in the manga she is a shy student librarian. Also, Hiroto is Katsuya's verbal sparring partner instead of his crony in Toei's anime.