for anyone else who wondered:
The Cigarette Smoking Man (CSM) is one of the more mysterious villains whose true motives are never quite revealed. Always in the shadows, pulling strings and covering up conspiracies, Cancerman always managed to elude Mulder and Scully in their investigations. What we do know of him is that he was a powerful figure who worked for the Syndicate, an organization that helps cover up the fact that aliens have visited Earth and are planning an invasion.
The Cigarette Smoking man was played by William B. Davis.