Liam O'Connor was a Special Agent training new recruits at the FBI Academy in Quantico. Eventually, he was promoted to the position of Assistant Director, having replaced Miranda Shaw and later, to the position of Deputy Director. He, like many of those that work in the FBI, believed Alex Parrish was guilty and is believed to have fallen for her while she was training at Quantico. However, later in the events of Quantico, it was revealed that Liam was the terrorist, using the voice of every agent from Alex Parrish's class while coercing agents to assist in his attacks. He was portrayed by Josh Hopkins.