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.
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).
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.
He later becomes a founding partner at Sterling Cooper Draper Pryce.
Draper is the series' protagonist, and more storylines focus on him than on other characters.
When, in Season 6, Peggy shares Stan's SCDP insider information with Ted, noting that the Heinz Ketchup executive had met surreptitiously with SCDP but there was friction between him and Heinz Beans executive Raymond Geiger (an SCDP client).
Ted sees an opportunity and pressures Peggy to "find out everything you know about Heinz Ketchup." In "To Have and To Hold", Chaough's team encounters Don's in the hallway in front of the room where firms are making their Heinz pitches, and Don is shocked to see Peggy there—in the end, Heinz chooses a third (larger) firm, and Raymond Geiger drops SCDP because he feels betrayed.
Don promotes her to copywriter, and she eventually accepts a copy chief position with Ted Chaough's firm, CGC, only to find herself once again working for Don following a merger.
Peter "Pete" Campbell (Vincent Kartheiser) is an ambitious young account executive whose father-in-law controls the advertising for Clearasil, a Sterling Cooper account.
Margaret "Peggy" Olson (Elisabeth Moss), upon introduction, is the ostensibly naïve "new girl" at Sterling Cooper.
She was originally Draper's secretary, but showed surprising talent and initiative, including a knack—similar to Draper's—for understanding the consumer's mind.
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.