Greiger, known as Bommer in the Japanese version, was initially one of Goodwin's five Dueling Assassins as well as a member of Iliaster. Later, he became a member of the Dark Signers, bearing the dark mark of the killer whale and having his "Earthbound Immortal Chacu Challhua" (however, in Z-one's timeline he was not a Dark Signer[3], as a recording file implies).

An honorable Duelist, Greiger was prideful, yet stoic. Likely of South American origin, he came from a destitute village and Dueled to provide financial aid to it. He was transformed into one of the Dark Signers when Roman killed him by hanging him over the Negative Ener-D. When his "Earthbound Immortal Chacu Challhua" was Summoned, it held the souls of his siblings and other children from his village. After Goodwin's defeat, he was brought back to life and learned that the Dark Signers were responsible for the destruction of his village

Greiger grew up in a poor village near the Nazca Lines. He looked after a group of orphaned children, along with his younger siblings Annie and Max.

One day, his village was destroyed in a massive fire and the children, including Annie and Max, were killed in the process. It was thought that Iliaster had used Greiger's village as the site of an "experiment" to summon the Crimson Dragon, which completely destroyed the village and killed his entire family. With such information that Iliaster didn't want anyone to know, Greiger then became involved in some sort of compromise with Rex Goodwin, and agreed that KaibaCorp would provide aid for the reconstruction of the village in exchange for exposing the Signers during the Fortune Cup.

Unbeknownst to him at the time, the Earthbound Immortals, mainly "Chacu Challhua", had caused their disappearance. Which is why Greiger is a good person who need to warn Yusei about the Earthbound Immortals