[[D.W. Read|Read Dora Winifred "D.W." Read] is Arthur's little sister and is a middle child. She attends preschool and enjoys watching children's television shows much to Arthur's annoyance. She is also known for her many short-lived obsessions and tantrums if these obsessions are not fulfilled. Many of the series' plots revolve around tensions between D.W. and her brother, and she is naturally better than Arthur in some activities such as fishing, which causes her brother to envy her. At times, she can be self-centered, annoying, says cruel things to Arthur and other people, and always tries to get Arthur in trouble, and make him look bad. But other times, she does show appreciation for Arthur being her older brother. She goes by the nickname "D.W." due to an evident dislike for her full name.She is the main antagonist.
Dr. Frederique Figue: Once taught Arthur piano lessons and later filled in for Ms. Krasny to take Mr. Ratburn's class to Crown City for a singing chorus field trip. He was a chorister as a child and later sung with Whiffenpoofs, implying he attended Yale University. He is also an extremely strict teacher and "fires" many of his students.