Yami Yuugi "Pharaoh, Nameless Pharaoh, Yami No Yuugi, The Other Me, The Other Yugi"

About

Age: 3000+
Blood type: A
Height: 153 cm
Weight: 42 kg

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

In Battle City, Yami discovers who he was in the past: He was a Pharaoh ruling in Ancient Egypt, according to Ishizu. In order to find out about his past as a whole, he must gain the three Egyptian God cards—Osiris (Slifer the Sky Dragon), God of Obelisk (Obelisk the Tormentor), and Sun God Ra (The Winged Dragon of Ra) during the Battle City tournament. Along the way, he runs into Noah, who has a grudge against the Kaiba brothers, and various pawns of Marik, his enemy in Battle City.

After Jounouchi collapses after his duel with Marik, or rather, his dark self, in the finals at Alcatraz Tower, Yami finds an even stronger incentive to duel him, but has to go through Seto Kaiba first. As expected, he defeats Kaiba and goes on to duel Marik, defeating him after an intense battle.
Doma Arc

In the Doma arc, things become more emotional for Yami. After he had failed to go into the Memory World due to the God cards 'not responding,' he finds that all the Duel Monsters have been turned into real life monsters. In his duel against Grimo, he finds out about the Seal of Orichalcos and its effect to take the soul of the loser of the duel. Unfortunately, after his duel with Grimo, his god cards are stolen by Raphael, Amelda, and Varon, people who work under Dartz's command. Dartz seems to be the new enemy of Yami's.

In his duel with Raphael, Yami is shocked to find the Seal of Orichalcos in his hand after he and Raphael exchanged cards due to a magic card's effect. In a desparate pinch, he activates the card, despite Yuugi's protests, and is under complete control. However, Raphael manages to defeat him. But before Yami's soul could be taken, Yuugi pushes him out of the way and his soul is taken instead, leaving Yami in a somewhat depressed state. However, Jounouchi quickly snaps him out of it by the form of a punch in the face, shocking everyone very much.
Memory World

After a historic battle against Zorc Necrophadius, he had sealed his soul along with Zorc in order to save Egypt. He had lost his memory as a result.
In the memory world, most of Yami's priests respected and loved him. Simon protected him, Mahad and Mana followed him, and Seto saw him as his best friend and rival. Yami sacrificed his psychic powers in order to protect Egypt. But his uncle tried to make Seto take his throne from him. In the end, he summoned the Horakhty with his own name, eliminated Zorc, and completed the mission during his lifetime. Seto carved a memory tablet in memory of him.

His real name is revealed to be Atem at the conclusion of the arc.

(Source: Yugipedia)