Yuugi Mutou is the main protagonist of Yu-Gi-Oh! Duel Monsters. At the start of the series, he is a shy boy who is really short for his age, something he always gets teased about in school. For this reason, he was always alone. However, his grandfather gives him the Millennium Puzzle prior to the story's time line and Yuugi is told that if he solved it, one wish of his could be granted. He manages to solve the Millennium Puzzle and he asks for friends and his wish is immediately granted. He also awakens the spirit residing in the Puzzle, but Yuugi is not aware of this until much later in the story.
When Yuugi does become aware, he and the spirit become very close, with him calling the spirit "Mou Hitori No Boku"—The Other Me—and the spirit calling him "Aibou'—Partner. Yugi then becomes a vessel for the spirit and he is told that his duty is to help the spirit find his lost memories. With the help of his friends, he helps the Pharaoh regain his memories while overcoming the most difficult of situations.
Yuugi is mostly seen living with his grandfather, since his parents are mostly on business trips. His mother, Ashita, makes a very brief appearance in the beginning of the second season, when Yuugi argues with the spirit. Yuugi is also very gifted as a duelist with the Duel Monsters card game, thanks to the expertise and upbringing of his grandfather.
Yuugi's deck, throughout the series, was really his grandfather's, since his grandfather gave him his deck in episode 1 to battle Seto Kaiba. However, in the last season—Pharaoh's Memory—he uses his own deck, which contains magicians, spell-casters, and machines.
Yuugi is also seen as a "Ladies' Man" in the series, according to the KCGP filler. However, from the beginning, it has been obvious that he has a crush on Anzu Mazaki, his childhood friend.
Yuugi Mutou makes several apperances in Yu-Gi-Oh! GX. He is first seen as a grown adult in the first episode, whom Judai Yuki runs into on his way to the entrance exam at Duel Academy. Yuugi then hands him Winged Kuriboh and walks away. There are also several mentions of him throughout the series.
In the final episodes, 179–180, he appears again to Judai Yuki, telling him that he has come to help Judai regain what he had lost in the last couple of years, which was the ability to have fun while having a duel. The older Yuugi then helps Judai Yuki reach a time period in between Battle City and Doma Arc. A completely different Yuugi runs into him and he is challenged to a duel, which he readily accepts. Yuugi then notices Judai's strong magical powers as does the spirit, so he lets the spirit take over the duel.
Yu-Gi-Oh! The Movie - Ultra Fusion! Bonds Over Time and Space!
Yuugi is one the main characters in this 10th Anniversary special of Yu-Gi-Oh! He, along with Judai Yuki of Yu-Gi-Oh! GX and Yusei Fudou of Yu-Gi-Oh! 5D's, battle Paradox in order to save Duel Monsters and the existence of time itself.
In one of the 5D's openings, it is shown that Yuugi had lost his grandfather's life during one of Paradox's assaults on his time frame and he is extremely distressed over the fact.
Henshin a go go baby! Transformation is a staple in many genres of anime, from fighting to magical girl. The sacred rule of transformation is that no other character is allowed is interrupt while you power up to your next form, so of course you want to make things spiffy with a henshin sequence.