Yugi possesses the three thousand-year old (five thousand in the English dub) mystical [[Millennium Puzzle]], which allows his body to bear host to the spirit/soul of the Puzzle, [[Yami Yugi]]. Yugi was initially unaware of his existence and control of Yugi's body, and partial or complete control of his mind, would involuntarily shift to Yami when Yugi himself or his best friends are in danger, or when Yugi is under emotional stress or mad.

He lives with his paternal grandfather, [[Solomon Muto]], and his [[Mrs. Muto|mother]]. In the manga, Yugi's father is living away from his family on business.