User: Who is the antagonist on The X-Files?
Assistant: There are many antagonists on The X-Files, but the most long-running individual antagonist is The Cigarette Smoking Man (CSM) also known as C.G.B. Spender. He was primarily responsible for orchestrating conspiracies. He was a member of "The Syndicate," which was a mysterious shadow government group that covered up the existence of extraterrestrial life.