Anthony Russek was an SD-6 agent.
Before Season 1Edit
Russek joined SD-6 early on when the Alliance of Twelve was beginning to form. He was the leader of various operations that involved agents stealing weapons, chemicals, and intel so they could be sold for money to fund other SD-6 operations. Unlike many other agents, Russek knew that SD-6 wasn't part of the CIA.
Russek was brought into SD-6 shortly after Sydney had discovered the Rambaldi Machine Code. Both he and Sloane talked about Rambaldi briefly before Sloane abruptly asked how Russek's wife was doing, to which he replied "good." He later appeared during the briefing about the Golden Sun, and showed up again during the briefing to spy on Luc Jacqnoud (A Broken Heart).
Russek didn't show up again until shortly after Dixon was wounded by K-Directorate agents. Russek filled in for Dixon while he was in the hospital, running reconnaissance while he and Sydney traveled to Geneva to recover the funds from Hassan's bank account. However, during the mission, Marshall discovered that there was a second transmission coming from the location. He reported the transmission to Karl Dreyer, who later reported it to Sloane (Mea Culpa).
Sloane sent a few agents to capture Sydney and held a private meeting with Russek. In order to get Sydney to confess she was a double agent, Sloane told Russek that he was going to be captured alongside Sydney and would have to be tortured to convince her that they were being serious. Although Russek tried to persuade Sydney to tell the agents the truth so he wouldn't be tortured to death, she remained silent because she knew he was lying. Just as Sydney was about to be tortured, she was released; Marshall found out that the transmission was coming from Russek and being sent to K-Directorate. Russek was quickly taken again and tortured (Spirit).
It was later confirmed that Russek had been killed. However, after talking to Jack, Vaughn found out that Russek wasn't a traitor after all. Jack had manipulated the transmission to make it look like Russek was a double agent working for K-Directorate (Spirit).