The Only Sane Man makes other people normal just by being around them.
Do We Have This One? In order to best allow a Dysfunction Junction to shine, many writers will introduce a Straight Man as a Foil. By letting the Straight Man act as only sane person in the cast, the audience can see just how crazy and wacky the other characters are, sometimes to the dismay of the normal character. However, this version of the character serves an additional purpose which may or may not co-exist with the original. As the only "normal" character in the setting, this person acts as a voice of reason or a stark contrast to the crazy the rest of the characters are dealing with. In these stories, the rest of the cast had absolutely no idea that they were behaving oddly or had any sort of issues. But seeing this character, and how well-adjusted they are, makes them question themselves and ultimate become more normal themselves.