Yami Yuugi (闇の遊戯)

Background

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.

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 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

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