The Cigarette Smoking Man reference article from the English Wikipedia on 24-Apr-2004
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Cigarette Smoking Man

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"The Cigarette Smoking Man" (the CSM) is a fictional character played by William B. Davis on the 1990s television series the X-Files. The character is known initially only by this nickname because he is almost always seen chain-smoking Morley cigarettes, and is usually surrounded by clouds of smoke.

On the surface, it may seem that the CSM merely tries to antagonize Fox Mulder and Dana Scully, but there's much more to him. He's involved in the Consortium, a shadow organization within the United States government that exists to hide from the public the fact that aliens are visiting Earth. The CSM is the one who knows the truth, and Mulder is the one trying to find it out. However, CSM's reasons are much more complex than simply the desire to hide the truth. Therefore, the character can not be described as purely 'good' or 'bad'.

In the final seasons of the series, his real name is revealed to be C.G.B. Spender. Also, one of the final episode confirms that the CSM is the real father of Fox Mulder.