Robby Ressler is the older brother of Donald Ressler.
When they were young, Robby was actually the responsible child, while Donald was a rebelious teenager who used drugs and alcohol and was always getting into trouble. On the other hand, Robby enlisted in the police academy and sought to become a cop just like his father. However, everything changed when Donald and Robby's father was killed in a staged shooting set by his partner Tommy Markin. After Donald learned that Markin was behind his father's murder, he confronted and shot him with his father's gun. Desperate, Donald called Robby to help him deal with what he had done. Robby chose to protect his younger brother and covered up his crime and eventually finished Markin off when he found out he was still alive right before he was going to bury him, but not before taking from Markin a confession of what he had done to his father. After this fateful event, Robby and Donald's lives were almost entirely exchanged. While Donald decided to improve, follow his father´s footsteps and become a cop, Robby left the police academy and started having troubles holding a job or keeping a business intact. After Donald went to D.C to become a FBI agent, the 2 brothers became estranged.