The incredibly FABULOUS alter-ego of our protagonist.
Téa is incredibly fixated on friendship, and honestly believes it's the ultimate source of power and can right any wrong, God bless her. His friends thought he died, but in the end he got better. She also happens to have enormous breasts, which are objects of pride for her and obsession and mockery for everyone else.
She can and will make speeches about friendship when provoked, and if she focuses on a single target, well..less said, the better. He is desperately in love with Serenity, but is mostly helpless compared to the raw sex appeal of Duke. An unashamed selfish egomanic, Kaiba yearns to crush Yugi in a duel, and in the meantime flaunts his money because he can. His most notable contribution to the series is coining the phrase Screw the Rules, I Have Money! He's frequently told to shut up and gets kidnapped a lot, and Kaiba is completely flippant about it at this point. In Season 4, she suddenly gets a change of voice and a rather expanded characterisation.
The mystery of his real father and his true identity is an occasional Running Gag; he may be a robot built in Ancient Egypt. Marik's sister and holder of the Millennium Necklace, who helps the heroes foil his plans.
She knows that there is a darker plot brewing, however, and her actions are to avert a terrible disaster she senses in the future; the cancellation of the series.
Compare/contrast the Character Sheet for the source anime.