Yami Bakura

Yami Bakura, also known as Dark Bakura, is the evil spirit of the Millennium Ring, and the main antagonist of the original "Yu-Gi-Oh!" series. Yami Bakura appears as a recurring secondary antagonist for most of the series, until the final arc where he is the main antagonist. Through the Millennium Ring, Bakura Ryou became a host to the spirit, allowing Yami Bakura to possess Bakura; even able to mimic his host's personality almost perfectly to the point that he is able to fool Bakura's friends. Yami Bakura is the longest running and most prominent adversary in the entire series, being an antagonistic counterpart and a great adversary to Yami Yugi.