Throughout the course of the series, Joan has a long-standing affair with Roger Sterling, which results in their conceiving a son.
She ascribes the boy's fatherhood to her husband, a physician serving as a military officer in Vietnam, whom she later divorces. (John Slattery), was one of the two managing partners of Sterling Cooper, and later a founding partner at Sterling Cooper Draper Pryce (SCDP).
After obtaining a divorce from Don, she marries Henry Francis and moves to Rye in late 1965.
Despite no longer being married to Don, Betty is shown to harbour feelings for him. Harris (née Holloway; Christina Hendricks) is first depicted as an office manager at Sterling Cooper, who acts as a professional and social mentor, as well as an occasional rival, to Peggy Olson, much as Don Draper is to Pete Campbell.
Peter "Pete" Campbell (Vincent Kartheiser) is an ambitious young account executive whose father-in-law controls the advertising for Clearasil, a Sterling Cooper account.
Born with a silver spoon in his mouth, he becomes more competitive with Don as the series progresses, and ultimately becomes a partner of Sterling Cooper Draper Pryce.
Draper is the series' protagonist, and more storylines focus on him than on other characters.
Margaret "Peggy" Olson (Elisabeth Moss), upon introduction, is the ostensibly naïve "new girl" at Sterling Cooper.
However, by the next morning he changes his mind and pleads with Don to send him to California to work the new Sunkist account for SC&P.He also insists that because of his attraction to her, he must remain reserved in her presence.However, they ultimately begin a relationship and are not very subtle about it; they're seen giggling and paying attention only to each other in the office, which annoys many of their colleagues.After Don embarrasses Ted and Peggy in front of a client, Ted decides that he cannot be around Peggy anymore.However, seeing her dressed provocatively to go on a date with another man, Ted camps out at her door until she returns.SCDP's partners (except Don, who disapproves) negotiate to reward her for engaging in a sexual tryst with a client by making her a partner. Roger's relationship with Lucky Strike, one of Sterling Coopers most lucrative accounts, is key to the story from the outset.