Yu-Gi-Oh! is a Japanese manga created by Kazuki Takahashi, which has spawned a franchise including multiple anime series, a trading card game, and numerous video games. Most of the incarnations of the franchise involve the card game called Duel Monsters (originally known as Magic & Wizards), wherein each player uses cards in order to defeat one another.
The main character of Yu-Gi-Oh! (all anime, manga and movies except Yu-Gi-Oh! GX) is Yugi Mutou (Yugi Moto in the English anime), a shy, pure-hearted high school student and gaming expert who possesses an ancient Egyptian relic called the Millennium Puzzle, and the Nameless Pharaoh (Namonaki Pharaoh in Japanese) or Dark Yugi (Yami Yugi, also "the other Yugi" or, later on, "Atem", his real name, revealed only near the end of the series), a darker personality held in the Puzzle. Yugi's best friends, Katsuya Jounouchi (Joey Wheeler), Anzu Mazaki (Téa Gardner), and Hiroto Honda (Tristan Taylor) are also primary characters, as well as Dark Yugi's main rival, Seto Kaiba.
The main character of Yu-Gi-Oh! GX is Jaden Yuki (Judai Yuki in the Japanese versions), an energetic boy who possesses great talents in Duel Monsters.
Yu-Gi-Oh! GX follows the story of Jaden Yuki (Judai Yuki in the Japanese version), a young talented duelist who is given the card "Winged Kuriboh" by Yugi before Jaden's admission to Duel Academy (Duel Academia in the Japanese version), an elitist boarding school established by Seto Kaiba. Jaden, receiving low marks in his admission tests, is placed in the Slifer Red dormitory (Osiris Red) reserved for students with the lowest grades. The story goes on as Jaden faces challenges from different students in Duel Academy, and later finds himself entangled in a conflict related to the hidden secrets of the academy.