Main Cast:
* Jon Hamm as Don Draper
* Elisabeth Moss as Peggy Olson
* January Jones as Betty Draper
* Christina Hendricks as Joan Harris
* Vincent Kartheiser as Pete Campbell
* Rich Sommer as Harry Crane
* Jared Harris as Lane Pryce
* Kiernan Shipka as Sally Draper
* Robert Morse as Bertram Cooper
* Bryan Batt as Salvatore Romano
* Aaron Staton as Ken Cosgrove
Recurring Characters:
* Alison Brie as Trudy Campbell
* Michael Gladis as Paul Kinsey
* Jay R. Ferguson as Stan Rizzo
* Jessica Paré as Megan Draper
* Ben Feldman as Michael Ginsberg
* Matt Weiner as himself (appears as a character in a few episodes)
Notable Guest Stars:
* Maggie Siff as Rachel Menken
* John Slattery as Roger Sterling
* Linda Cardellini as Sylvia Rosen
* Bobby Cannavale as Henry Francis
* Rosemary DeWitt as Midge Daniels
This is not an exhaustive list. Many actors had recurring roles in different seasons, and there were countless other actors who appeared in guest roles.
If you're interested in learning more about specific characters or their roles in the show, you can always search for them on websites like IMDb or Wikipedia.