Yami Yuugi is the spirit of the ancient Pharaoh residing in the Millennium Puzzle. His past is shrouded in mystery. 3,000 (5,000 in the dub) years later, Yuugi Mutou, after trying to solve the puzzle for eight years, awakens the Pharaoh from his slumber, although Yuugi does not realize this until much later in the story. At the end of Duelist Kingdom, the Pharaoh asks Yuugi to help him recover his memories and Yuugi agrees to help him.
In the early manga, Dark Yugi starts out as an merciless vigilante. He emerges to deal justice to people who trespass the souls of Yugi and his friends. Although his acts are righteous, he lives up to his namesake of Dark; his Penalty Game punishments are usually very brutal. Later, while living inside Yugi's body, he seems to become more of a caring, nice and friendly disposition, even though he always had that in him, and the friendship of Yugi's friends had helped it be revealed to others. Yami is a strong, powerful and skilled Pharaoh. He attempts to balance darkness and evil in his use of the Shadow Magic from his Millennium Item. Unlike Yami Bakura and Yami Marik, he never uses it for personal gain, instead preferring to help others in need, and to inflict punishment only on people who have severely wronged innocents. He is slightly reserved, as he doesn't reveal his existence to Yugi or his friends. At first Yugi feared Yami Yugi, but after Yugi admits to thinking "another Yugi" exists inside him, his friends become aware of his existence and accepted him as a friend. Even before, Yami is extremely protective of Yugi.
Yami's pride is his greatest strength and weakness. Initially he refuses to lose games, because it would cause him to lose the chance to save Grandpa. This has caused him to almost kill Seto Kaiba by attacking his monster while he stood on a ledge and the shockwaves could cause him to fall if Yugi chose to win the Duel (in the Japanese version, Kaiba threatened to commit suicide should he lose). Learning how to lose became an essential aspect of Yami's journey, which he is tested in the Battle Ritual. Yami is also wise and intelligent. He knows all the rules and details of how the game is played, as well as those of all games. He also knows several special game techniques, such as the Double Hit dice roll technique, which, when two dice are used and the one with the weak spin stops first, lets him make the dice that's already spinning hit the one that isn't, allowing him to change its number, which is done by bumping the field with a body part, e.g the elbow. Despite being an ancient Pharaoh, Yami is very quick to learning and utilizing modern technology. He, despite initial shock, was able to quickly grasp the concept of holographic technology, how Dueling Arenas and field Power Bonuses worked, was able to use the Dungeon Dice Monsters Help computer to quickly formulate strategies, and was able to use Duel Disks flawlessly on the first try. Yami is also capable of translating the hieroglyphics of the Egyptians, figuring out the riddles or clues and what they mean. Through Yugi and his friends, Yami Yugi learns the values and powers of friendship and unity. After seeing Yugi overcome Marik in his Duel with Jonouchi, who has been possessed, Yami thinks to himself, he learned something from Yugi; that in kindness lies the greatest strength of all; one day Yugi will surpass him. Also, Yami has been protecting Yugi, and Yugi has learned from him the spirit of "never shrink back no matter how difficult it is". At the end of the story, Yugi grows enough to be self-reliant, and Yami's soul gets freedom.
Battle City
Doma Arc
Memory World
(Source: Yugipedia)
