Before there was the
mass media marketing ploy that is the TV
dub of Yu-Gi-Oh! (which, incidentally, only shows the
Duel Monsters-centered second season onward of the
anime series), there was the original
manga by Kazuki Takahashi.
Yu-Gi-Oh! tells the story of Yugi Mutoh (or Moto, in the U.S.), a slightly geeky high school student living in Domino City. He gets picked on a lot, even by his two friends Katsuya Jounouchi (Joey Wheeler in the U.S. version) and Hiroto Honda (Tristan Taylor), who are quite the troublemakers in the early volumes of the manga (chasing girls and getting into fights, among other things). Probably his only real friend at first is his classmate Anzu Mazaki (Tea Gardner), the token cute and sympathetic girl. All that changes, however, when Yugi manages to assemble the mysterious Millenium Puzzle, a gift from his grandfather Suguroku Mutoh (Solomon Moto, or just "Grandpa"). He is "gifted" with another self, a stronger, more confident identity who wields the power of the "Shadow Games", using it to dispense harsh justice to the people who threaten Yugi, or his friends and classmates.
As many anime fans may note, the early episodes of the manga are significantly darker than the anime series (even in comparison to the original Japanese). In the first volume alone, Yugi challenges a corrupt hall monitor, a conniving "reality TV" director, an escaped murderer, a karaoke-loving bully, and others to Shadow Games (ranging from dice-rolling, to a high stakes version of "The Quiet Game", to my personal favorite, a game of air hockey on a hot grill with a puck made from ice that has a tube of nitroglycerine stuck in it), where the contestants risk losing their lives or their minds (Yugi frequently inflicts a "Penalty Game" illusion, such as amplifying the karaoke-obsessed bully's heartbeat to deafening levels, or making the world look like one big censor mosaic to the evil director). Duel Monsters (originally called "Magic and Wizards") isn't even mentioned until volume 2 of the manga series. As you can probably tell, I find the manga to be a vast improvement over the stateside release of the anime (I'll admit I'm biased, though, since the manga is uncut and I haven't seen the Japanese version of the anime).