|“||Had enough of life?||”|
–Ari, The Angel Experiment
Unlike the other hybrids, Ari spent his early life as a non-mutant human. When he was three years old, Jeb disappeared along with the Flock, leaving Ari at the tender mercies of the School's genetic scientists. The geneticists used Ari as an experiment, splicing his DNA with that of a wolf in order to create a new breed of Eraser that could live longer than the previous versions (those whose DNA had been spliced in the womb). But Ari didn't turn out as well as the scientists had hoped.
Despite his young age, Ari is the size of a full-grown human because of the genetic engineering performed on him by the School. He is always in a partially morphed state; not quite human and not quite wolf, he is the most "wolf-like" of all the Erasers.
In the first book, Ari's traits seem to be quite adult-like, while in the second book, the reader discovers his feelings and thoughts are often like those of his seven-year-old self. This is best shown when he goes to Best Mart in the second book, where he steals a Game Boy and is also disgusted by a woman holding a bra in public.
Ari also exhibits slight masochistic tendencies, as illustrated when he bites himself several times in School's Out Forever, because the pain "felt better."
In School's Out - Forever, it is revealed that Ari has a strong (but reluctant) admiration for Max. He even comes up with a plan to steal Max away, so she could 'read to him and play games with him'. However his wolfish-seven-year-old self shows through when he adds that he planned to cut off her wings.
Angel informs Max that Ari loves her, loves her a lot, although he constantly tries to kill her. Max's reaction was something like: "Jeez. Ari loved me? Like a little kid? Like a big Eraser? Was that why he kept trying to kill me? He needed to read an article about how to send clearer signals."
Ari wants Max to be his friend, although he tries to wound Fang to the point of hospitalization because he doesn't seem to like Max with Fang. He considers just taking Max as his friend, and the two will live together somewhere in hiding.
Ari and Max share many similarities, the most obvious being that they are both mutants and both hear "the Voice" in their heads. In The Angel Experiment, the possibility that Ari and Max are siblings is discussed.
Ari's greatest desire is to have his father be proud of him, and is extremely and horribly jealous of how his father dotes on Max. He one time expresses a desire to choke his father until Jeb realizes he ought to pay more attention to him. His father is proud of him in School's Out Forever when Ari tells him of his plan to steal Max, however.
While fighting in the New York sewers, Max accidentally snaps his neck and he supposedly dies.
In this book, Ari, despite having been killed in the previous book, comes back to life after the School fuses the bones in his neck; he also has wings retrofitted on him by the whitecoats (though it is later said that his wings don't work right and are very painful).
While Max is having ice-cream with Sam, he is seen with Max II for the first time.
Ari joins up with Max's half of the Flock in this book. While the other Erasers were "retired" (killed), the whitecoats allowed Ari to continue to live, as his expiration date had recently appeared on the back of his neck, indicating that he'd die on his own anyways. After learning that his death is approaching, Ari becomes extremely depressed and seems to lose his hatred of Max and the Flock.
When the Flock is held captive in the School, he shows Max some of the experiments and tells her of the whitecoats' plans for Re-Evolution, saying that even though he knows he will die soon, he hopes that the Flock can still escape and stop it.
He helps Angel find Total (who the whitecoats took from the Flock) and breaks open a cage that they're trapped in. Realizing that the white coats will probably kill him for helping them escape, Max asks Ari to join them, much to the displeasure of the rest of the Flock (except, perhaps, for Angel). Ari is very grateful to Max for taking him in and promises to keep her safe. He joins Max's "mini-flock" when the Flock splits and goes with her, Angel, Nudge, and Total to Europe. During this time, Max notes that he doesn't talk much, as if he didn't think he had a right to an opinion.
It is revealed that, because Jeb is Max's father, Ari is her half-brother.
Ari tries to back up Max during her tests against Omega; and later, when a mutant riot breaks out, he uses his strength to literally "toss smaller mutants into the mosh pit of death". In the midst of the fight, he suddenly collapses. Max tries to find where he was hurt, but he wasn't injured. His time has run out and he suddenly expires.
At the beginning of the book, there is a memorial held in his honor by the Flock and Jeb is at Ari's make-shift funeral. Each of the flock drops dirt onto the casket, and Angel, the Gasman, Fang say a few words. Most of the Flock -- primarily Max, Nudge, Total, and Angel - break down and cry.
After his death, many villians bring Ari back to intimidate Max, such as Mr. Chu -- who had dug up Ari's body and combined it with robotic parts -- but have utterly failed -- Mr. Chu failed due to one of Gazzy and Iggy's bombs.
In Nevermore, Ari is cloned perfectly (retaining all of his memories) and kills Maya; however, he is killed by Dylan when he attempts to kill Fang. This is the last time Ari is seen in the series, though Jeb's survival and Angel's words suggest that he was recreated again after the book ended.