Yugi Muto

Yugi Muto (voiced by Dan Green) is one of the two main protagonists of Yu-Gi-Oh!. When Yugi's grandfather gave him an box containing the Millennium Puzzle, after solving it, he awakened the ancient spirit within it named Yami. Whenever Yugi starts a Duel, Yami takes over to Duel for him.

Adventure series
After being separate from his friend Yugi, Yami returns from the Afterlife to spend the rest of eternity with Yugi. The two fuse together and become one being (Yami becoming the dominant half).