Cyber Kaiba is a character appearing only in the Yu-Gi-Oh! novel.
He appears to be the real Seto Kaiba and invited Yugi to duel him at the top floor of KaibaCorp. Yugi accepts and duels Kaiba. Mokuba interrupts the Duel partway through, telling Yugi that it is not the real Kaiba, as Kaiba has not yet awoken from his catatonic state. The Kaiba that Yugi is playing against is actually a Cyber Kaiba, controlled by the KaibaCorp computer, using all of Kaiba's memories.