The strange dark spirit that lies inside the Millennium Ring. He searches for all the other Millennium items. Although the purpose is unknown, it's obvious that the intent is pure evil. When in full possession of Bakura's body, he is capable of invoking many magical powers of the World of Darkness into this world. The spirit has linked itself through the Millennium Ring to Bakura and is able to return itself to Bakura even if discarded or lost.
He's the main arch enemy of Yami Yugi. He holds a 5,000 year old grudge with Yami Yugi.
It is revealed that the reason for this grudge was that Atem's (Yami Yugi's true name, and his life in Ancient Egypt) father sacrificed Yami Bakura's entire village to create the Millennium Items. Since Atem's father died, Yami Bakura wanted to get revenge on Atem/Yami Yugi for what his father did.
Yami Bakura uses an occult deck focused around Fiends & Zombies to unleash powerful dark magics.
They say that revenge is sweet and that it is also a dish best served cold. This also happens to perfectly describe ice cream. Come take a look at characters who are sustained by their vengeance and not just ice cream.