The Imitator of Death, or Ghost Kaiba in the 4Kids dubbed version, is an extremely talented and demonic master of disguise and a minor antagonist in the Duelist Kingdom arc of the anime Yu-Gi-Oh!.
He is voiced by Tony Hirota in both of his forms, while in the English dub, he is voiced by Eric Stuart as Ghost Kaiba (who also voiced Seto Kaiba, but with his voice digitally altered to make it sound more demonic) and Wayne Grayson in his true form, who also voiced Joey Wheeler.
Pegasus J. Crawford hired this strange figure to duel Yugi. The Imitator of Death had the appearance of Seto Kaiba, except with dark shadows under his eyes, and his voice sounded strange. He was using the real Kaiba's deck, as it was stolen from him by Pegasus' goons after Kaiba's supposed death. However, Yugi managed to defeat the first Blue-Eyes White Dragon, but the second would have beaten Yugi, had Kaiba not hacked his impostor from his computer. In the end, it was Kaiba using the Heart of the Cards that destroyed the second Blue-Eyes. At this point, it was revealed that Kaiba was alive, and the Imitator revealed his true form, which was a fat and ugly clown.
The Imitator of Death waited patiently until he drew his final Blue-Eyes, but Yugi was able to revive one of the destroyed Blue-Eyes with Resurrection of the Dead and powered it up with his Holy Elf, allowing his Blue-Eyes to destroy the Imitator's and take his life points down to zero, winning the duel. Yugi then used the Millennium Puzzle's power to make the Imitator disappear off the face of the earth.
In the 4Kids version, the Imitator was really Kaiba's ghost or his evil side and was sent to the Shadow Realm instead of Hell. In the manga, he does not even exist in the first place and it is a human ventriloquist who uses a Kaïba-like puppet who challenges Yugi with Kaïba's deck.