Acheron is the John Stamos of the Infinity world. He has a multisyllabic Greek last name, like Stamos's Full House character Jesse Katsopolis, and even though he's 11,000 years old, he doesn't look a day over twenty. Must be the yogurt.
Unlike Uncle Jesse, who dressed like Elvis and thereby had incredible fashion sense, Acheron dresses like an extra from The Craft. He has long black hair, he keeps his sunglasses on indoors, he wears a black T-shirt with a glow-in-the-dark skull on it, and he carries a black backpack with an anarchy symbol on it. We'd tell the dude to dress his age, but we're not sure how 11,000-year-olds dress.
Nick refers to Acheron as his "best bud" in the prologue, but we don't see them become friends in this book. Nick likes Acheron's car, and Acheron tells him a little bit about immortality, but for a character treated by everyone as if he were God's gift to humanity, he factors in very little in the plot. Other than the fact that he's an all-powerful immortal, we can't tell you anything else about him.
Acheron's phoned-in characterization may be a result of the fact that Sherrilyn Kenyon introduced him as a character in her Dark-Hunters series and expects readers to know him from those books.
Anyway, there's a lot of foreshadowing concerning Acheron and Nick's friendship. Or is it a frenemyship? "Stay away from him. Ash is evil to the bones. He will destroy you" (7.123)—that's what a voice in Nick's head says. The voice is Ambrose's, and Ambrose is Nick from the future. Ambrose believes that Acheron will eventually turn Nick evil. He can't be wrong right?
Yeah, the worst things our friends do is show up late to the movies, so we would have no idea how to handle this.
By the way, Acheron has a Charonte demon companion named Simi. Simi lives in a tattoo on Acheron's arm and seems to take human form later in order to protect Nick. She acts as comic relief with her funny way of talking. "Why are you sleeping on the ground out here, Mr. Boy Human?" (12.5), she says to Nick—cluing us in that she, herself, is not human.
Simi also carries around barbecue sauce because she seems to like to eat flesh and blood (with sauce), although we never see it happen in the book. She's also a character from the Dark-Hunters series. We have a lot of catching up to do.