Schiller was a KGB agent and use to be Tom Farrell's handler.
Schiller and his colleagues instructed Lieutenant Commander Farrell to seduce Susan Atwell, the mistress of the Secretary of Defense, David Brice, so he could blackmail him, however, it ended in getting her killed and compromising Farrell/Yuri's identity which got Dr. Sam Hesselman by Scott who than killed himself after David improvises with a story Scott killed Susan and lead everyone to believe Pritchard is Yuri due to Farrell blackmailing Brice with a printout linking him to Susan's death.
At the safe house, while Tom was being berated by his interrogators when the situation was "poorly handled", Schiller entered and request Farrell to return to Russia since America is no longer safe for him, but Farrell's feelings towards Susan were genuine and tells them he's done being their mole. Even with the interrogators holding him a gunpoint and Schiller telling him that he's a Hero of the Soviet Union can't sway him, Schiller lets him leave the KGB, confident that he'll return and he has no where else to go.
As of 1991, of the KGB being dismantled, Schiller and his colleagues returned to America to monitor Farrell.
As of 2011, after Tom declared to cut ties with them and left, David confronted him about Tom sending the printout to Director Marshall which lead to him resigning, he revealed himself to be Tom's handler before shooting him to death. After Brice's death being public, he than murdered former senator Billy Duvall after overhearing his connections to the KGB. Schiller and his colleagues than found themselves being targeted by the Anti-Hunters.
Lt. Cmdr. Thomas "Tom" Farrell
William "Billy" Duvall