(the following lines are spoken in a bored, monotone voice)
So it all started with archeologists, digging up an ancient Egyptian artifact of incredible power. The artifact ended up with a Japanese friend of one of the archeologists, who eventually settled down and opened a game shop. Now his grandson (a very cute little boy who is famous for having the most impressive hairstyle in the history of animation), found the artifact, and believing that it will grant him his wish, he begins to reassemble it. The artifact, a pendant resembling an upside-down pyramid, awakens the being known as the King of Games. An ancient pharaoh, who punished evildoers by challenging them to "games of darkness" that puts the players' life (or at least sanity) on the line. The young boy and his friends face many threats, including bullies, terrorists, criminals and gangs, all of whom call the wrath of the Pharaoh on themselves. However, things turn serious with the appearance of a green haired millionaire boy (who likes to screw the rules because he has money), starting a long lasting antagonism, that not only overtook the plot, but changed the world of non digital gaming forever, giving birth to the most popular trading card game of all time.
YuGiOh, is a fantasy/horror manga series created by game fan and Egypt enthusiast, Takahashi Kazuki. The manga was adapted into a 27 episode anime, by Toei Animation. The anime adapted the first seven volumes of the manga, modifying the plot of some episodes, removing others, and adding some that didn't appear in the manga. It also expanded the main cast with a fifth member, based on a one-shot character from the source material.
After the series by Toei, YuGiOh was picked up by Studio Galop, and Nihon Ad Systems, that relaunched the series as YuGiOh! Duel Monsters, dumping the old encounters already animated by Toei, and focusing on volumes 8+, bringing back several chapters from volumes 1-7 that were relevant to the later plot, and incorporating them into the plot. YuGiOh! Duel Monsters, was (sadly) licensed in the US by 4kids! Entertainment, that successfully killed the entire show for the whole world, but on the good side, indirectly spawned one of the funniest Web Original series ever. It was recently picked up by fans and most of the more important episodes are being re-dubbed as part of Project YGO. The new dubs are done far better than any American dubs I've heard so far.
The Duel Monsters Trading Card Game became a full game thanks to Konami, and a very successful one. I admit to be a collector of cards, even though I don't think I'll ever have the chance to play against anyone.
The series later spawned two spin-off/sequel series, GX and 5D. So far, I have only watched plain YuGiOh, and the first episode of the Project YGO dub. I'll wait till they release the second one, regardless of how long that will take, then I'll watch the rest with subtitles. If I can find them.