As it turns out, January Jones isn't the only "Mad Men" co-star who was considered for Peggy and ended up with another role on the show instead. The same is true for "Billion" star Maggie Siff, who would go on to portray fan favorite Rachel Menken on the show.
As Siff revealed to Cigar Aficionado, "Originally, I was supposed to read for the character of Peggy Olson [which went to Elisabeth Moss], but my manager said, 'I don't think you're Peggy. You're Rachel...So that's what I read for. They kept calling me back" (via ET).
Siff was a regular fixture on "Mad Men" for the first season, and then only made a few sporadic appearances throughout the rest of the series. However, she doesn't seem to have any regrets about playing a role that lasted for one season instead of seven. "When you read a pilot script, you're really just thinking about a pilot. You know...you never know if it's gonna go beyond that, and then if it does, what its life is, what the life of that character is," Siff revealed on "The Off Camera Show" (via Youtube).
Plus, Siff had a good feeling about her and Rachel Menken. "For some reason, and it just doesn't happen very much...I just knew that the character belonged to me. I was like, she's mine." Menken obviously was correct, and she helped cement that first season of "Mad Men" as a hit.
