Marcie is the perpetual sidekick of Peppermint Patty. She is a well-read girl who is terrible at sports, although she regularly plays on Peppermint Patty's team to avoid offending her best friend. Like Peppermint Patty, she has a crush on Charlie Brown - "Charles" to her - but she is a tad more direct in stating her feelings. Otherwise, she has no interest in boys, as shown by a particular encounter at summer camp. He catchphrase is calling her best friend "Sir", something Peppermint Patty claims to find annoying.