When a show has been on for many seasons, sometimes new faces are needed to mix things up. AMC period drama Mad Men — which is about to embark on the second half of its seventh and final season on Sunday (April 5) — was well known for refreshing its story lines with new characters each season. From new lovers for Don Draper to new clients (and partners) at Sterling Cooper Advertising Agency, the show's creators cast a gamut of guest roles.

As part of saying a bittersweet goodbye to the show, PopCrush retraced each season of Mad Men and highlighted 13 surprising and often unrecognizable stars who played a part, however minor, on the groundbreaking series. Check them out in the gallery above.