Robert was born in the Abnegation faction with his sister, Susanna Black, and are neighbors of the Priors. Their father works around the city, traveling around in his car, so he drives the siblings to and from school everyday.
He occasionally offers to drive the Prior siblings as well, but they courteously turn down, being the Abnegation children they are who would not want to inconvenience anyone. When their father has to work late, though, they take the bus home with Tris Prior and Caleb Prior.
He, along with Tris, sees the tentative flirting between their siblings, Caleb and Susanna.
At one point, Tris believed that if she didn't transfer, she would have ended up marrying Robert. Obviously, since both of them transferred to different factions, this was not going to happen.
During a delivery routine of the Amity trucks of apples into the city, Robert spots Tris on a Dauntless trip to the fence, peering at the back of the truck his fellow Amity initiates were sitting in. He calls her by her true name, Beatrice. Tris realizes that she didn't notice Robert's transfer during the Choosing Ceremony, thinking that he and other Abnegation members may have transferred after she and Caleb initiated it.
He awkwardly but happily hugs Tris, but comments that the Dauntless do not seem friendly when he notices the bruises on her face, and after Molly started teasing them, telling her that she could go back to Abnegation.
Robert is only mentioned in Insurgent, when Tris and company are at the Amity compound and she asks Susan if she has seen him yet. Susanna, in fact, has, and they grieved the death of their parents separately, with each other's own faction.
He makes a short appearance by the end of the book when Tris, Christina and Marcus Eaton approach the Amity for help; he is among the Amity, and Abnegation, who chose to leave their compound to help them protect the defenseless Erudite civilians from the attacking Dauntless and Factionless.