Yami Yugi and Yugi Mouto, The main characters in yu-gi-oh, are the hostess of the Millennium puzzle.
Yami Yugi is an Ancient Egyptian Pharaoh that sealed away the shadow games for a millennia, but then our dear little Yugi Mouto broke the seal and Yami was able to come out of the puzzle, and defened the world from the shadow games.
And if you're like me and watch the dubbed version of yu-gi-oh you'll also see that Yugi don't seem to know that Yami's there. and none of his friends seem to notis that his voice,clothes and hair style seems to change. And that Yugi went all weird after Yami tried to beat Seto Kaiba in a duel to get into the castle at duelest kingdom, just because Kaiba said that he'd jump off the ledge of the castle if Yami's Celtic Guardian took off one of the heads of his blue eyes ultimate dragon cause he wanted to save his little brother, Mokuba. but in the end Tia won his six more star chips from dueling Mai { because Mai let her win, and because she already had ten star chips.}and gave them to Yugi so he could enter the castle.
Little interesting details: *sigh* Anyway... all I know is that his favorite food is hamburgers :P
Yugi grew up in Domino City. He's a freshman at Domino High school, so he's 15 years old and is in class 1-B. He's small, shy, and he doesn't have much self-confidence. He used not to have many close friends, except tia, a childhood friend which he now has a crush on. Others like to pick on him a lot. That certainly didn't help him become more open... But as the adventure of the series unfolds, he gathers friends with whom he has a deep relationship of faith; first Joey, then Tristram, much later, Bakura, etc. He likes to play games a lot (it's his name after all! (yuugi = game)). He's really skilled and he can beat almost anybody. He has a treasure, the Millenium Puzzle, the golden pyramid pendant he always wears around his neck.
When he or someone he cares about is in danger, his alter ego, which appeared when Yugi assembled the Millenium Puzzle, takes control. The fans of the series have found many nicknames for him: Dark Yuugi, Black Yuugi, Yami(=darkness) Yuugi, Yûgioh (= the game king), etc. Physically, he basically looks like the regular Yuugi, but meaner. And unlike his alter ego, he has a lot of self-confidence (sometimes maybe a little too much *laughs*). He has a strong faith in his friends, and is ready to risk his life for them, as well as for honor (especially "the duelist's honor"... oh come on, it's paper rectangles!!!). He has usually a calm and serious temper, you know, 'keep it cool'. Something very charateristic about his temper, if you ask me, is when he encounters something difficult, he has a normal "oh no!!!" reaction and panicks, but then suddently his confident smirk comes back (kawaiiiiiiii ^,^; ) just to make the other mad hehehhh. Anyway... he hardly gets really mad, but when he does, let's just say that the person who made him angry should worry about their lives, or at least their sanity.
At the beginning, he had more like a maniac-like temper... Anyone who had threatened him or his friend would be challenged by him to a game, which the rules were modified since it was a 'yami no geemu' (game of darkness). This type of game can be played when at least one of the player has a Millenium Item (well, I guess). If the opponent loses (always hehehh), well he has to undergo the game of sanction. Basically, it's just a fancy name to say 'punishment'. And as I said earlier, it usually costs the looser their sanity, and even sometimes their lives.
The big question: where does Dark Yuugi come from? We don't know yet. But some elements seem to show that he was a pharaoh, back in ancient Egypt. We'll see.