Best Episode for Each Character (Any Series)?

Eventually every season focused in on one of the major characters of each series. If a newbie to a series asked you to sit him/her down, and show him/her the definitive episode for a character (in your opinion, this episode best represents said character, or had the most impact on said character), what episode would you pick for each character? Why? May be too ambitious to cover all series, but I'm interested in what you'd have to say. Free free to address certain characters/series. I just want to see other perspectives.