Speaking to TV Guide, Weiner explained that he likes the way Peggy (Elisabeth Moss) has developed over the series.
"She really ends up being Don's equal [in season four]," he said. "She's as smart and capable as anyone in the office, really.
"What a blast we had writing her character. She's so human, and to see her reaction to success and her reaction to conflict and a bigger chunk of her personal life that wasn't about her mum - it was a joy."
Weiner also suggested that he does not think of Peggy as a symbol for the women's movement.
"A lot of people were saying Peggy somehow represented feminism or the spirit of change, but I hope people realise none of these characters are meant to be symbols," he explained. "I love the line when she says to Abe, 'I'm not a political person', because it's so true. She may be changing the times, but only because she likes her job and she's succeeding at it."
Mad Men continues in the UK on Wednesdays at 10pm on BBC Four.