Little is known about GraveRobber, even though he's constantly seen in everyone else's business: He runs into Shilo Wallace in the graveyard and nearly gets her shot by GeneCops, then helps her escape from the festival only to drag her to a back alley full of Zydrate addicts. However, it is in this alley that he shows Shilo that Amber Sweet is addicted to surgery (and by extension, Zydrate), and explains to her the finer details of Mag's contract with GeneCo, thus alerting Shilo to the dangers of Mag's retirement.
GraveRobber takes an almost omniscient point of view during the course of the story, acting as a narrator at the beginning and end of the film, knowing of the dangers of the Repo Man caused by greed, then scorning people for letting grudges get out of control. He is also aware of the bloodbath the opera will become due to culmination of all of the plots taken by the characters (meaning he must be aware of most, if not all of their secrets somehow).
At the end of the story, GraveRobber scornfully questions why everyone can't move on, why grudges like the one between Rotti and Nathan have to go on, given how everyone ends up dead someday. He then begins to tell the epilogue of the tale, furthering his position as the narrator.
GraveRobber is a generally lively character. He goes about his job---both stealing zydrate from corpses and dealing it---with a smile on his face. Though his intentions for doing so are never made clear, he is very helpful to Shilo throughout the story when they interact. In his narrative songs, GraveRobber shows a very philosophical side, noting how people created the Repo Man through their own greed in Repo Man, then saying that holding grudges as Rotti and Nathan did is pointless, as people all end up in a "Tiny Pine Box" in Epilogue.
Though his intentions for doing so are never made clear, GraveRobber helps Shilo quite a bit over the course of the story. Though whatever trouble she gets into is usually caused by him in the first place, it usually serves a purpose. He gets her caught in the graveyard, but helps her evade the GeneCops for a short time. He brings her into the alley with the Zydrate addicts after helping her escape the festival, but shows her not only that Amber Sweet is addicted to Zydrate, but the danger Mag is in.The alley is raided by the GeneCops, then GraveRobber helps her get home. Terrance Zdunich has alluded to Graverobber's intentions with Shilo being sexual/romantic, explaining that the song lyrics for "Needle Through A Bug" (a deleted scene that plays during the credits of the movie) are all innuendo. He has also said that Graverobber's cry of "GRAAAAAAAVES" during "21st Century Cure" was to flip off authority and to impress Shilo.
GraveRobber's relationship with Amber seems to be one of mixed business and pleasure. He supplies her with the Zydrate that she's addicted to, and she supplies him with sex or money in order to obtain it. However, it could be seen that he only puts up with her as she is his biggest customer, as evident in At the Opera Tonight. During the song, Sweet berates GraveRobber for one more pre-show hit of Zydrate. He asks her to be patient, but she simply throws money at him. He impatiently hands her a vial of Zydrate and tells her to "Go get cut", with an irritated smile. During the song 'Come Up and Try My New Parts' We see Amber exchange Sex for Zydrate. Before the song in 'Can't Get It Up if The Girls Still Breathing' We hear Amber poke fun at the GraveRobber saying "Whats the matter GraveRobber? Can't get it up if the girl's still breathing?" Implying that the GraveRobber is a Necrophiliac, Though this is never mentioned again so it could have in fact just been a joke.
"21st Century Cure"
"At the Opera Tonight"
"Can't Get It Up If The Girl's Breathing?"
"Come Up and Try My New Parts"
"A Needle into a Bug"