|~ Muffy's famous catchphrase.|
She is voiced by Melissa Altro.
Muffy is an anthropomorphic monkey with tan skin. She has long, auburn hair which she usually has tied into twin braids with purple bows. In early books and episodes, she was depicted with buck teeth, these however were removed soon afterwards in the series as well as the later books. Her usual outfit consists of a purple, frilled dress with a lavender belt, with a white, long-sleeved blouse underneath, white knee-high socks and brown Mary Janes.
She wears a purple and white nightgown with a lavender robe and pink slippers for pajamas.
Because she is rich, she owns a variety of formal and semi-formal outfits which she has worn throughout the series.
Like her collection of formal outfits, she frequently has her hair styled differently as well, including a bob, bouffant, pigtails, or even just letting it down.
Like most of the main characters (including Arthur), she is 8 years old and in third grade. However unlike most of her friends, she tends to be snobbish and arrogant, likely attributed to her family's wealth. She believes that money, her butler Bailey, or her father can solve nearly every problem. Despite her negative side, she does regularly help and gives advice to her friends (usually if it involves money or fashion) and well as learns and respects moral lessons throughout their adventures.
Like Arthur's sister D.W., she can be quite authoritative at times.
In "The Cherry Tree", Muffy is shown to have feelings for trees and the environment after her beloved cherry tree is sawed down after her father makes a land swap with a neighbor so that she can install a huge bouncy castle and a tennis court.
Muffy moved to Elwood City while Arthur and Francine were in second grade. There she was assigned to their class and gradually became friends with them. Initially, Francine believed she was nothing more than a spoiled brat when she got her caught cheating on a test. Muffy soon began to feel guilty after getting her friend into the mess, and apologized by telling their second grade teacher Mr. Marco that she was the one who created the cheat sheets. The two reacquaint and become friends afterwards. Soon afterwards, she becomes friends with Arthur and his friends as well.
It is revealed in "Arthur's Birthday" that she and Arthur share the same birthday: May 25. Initially they are shocked to learn this and argue about which party all their friends should go to, but not long afterwards, they agree to hold their parties cooperatively for that year onward. Muffy is also of Irish descent.