Sentence:  She was the <WSD>straight man</WSD>, he was the comedian, and their audience was “standing room only” when they stepped up to the microphone. 
Meaning of the word marked with <WSD> tags:  A member (of any gender) of a team of comic performers who plays a supporting role by helping to set up jokes and punch lines through engaging in dialog with another comedian playing a more eccentric or otherwise more interesting character; a foil who plays such a role in theatrical comedy.