Each show begins with the reggae theme song, "Everyday, when you're walkin' down the street, everybody that you meet has an original point of view".
- Arthur, a third-grade boy aardvark
- D.W., his sister (4 3/4 years old)
- Buster, Arthur's rabbit friend
- Brain, an intelligent bear (once voiced by Steven Crowder)
- Binky, a British Bulldog and former bully
- Muffy, a wealthy monkey
Arthur has been gradually promoting a liberal agenda since Season 21. From that season is an episode, "Arthur Takes a Stand," featuring John Lewis as a guest star. There is also an Internet short, titled "Arthur on Racism: Talk, Listen, and Act," that was dedicated to John Lewis after his death.
The show met some controversy in the 22nd-season premiere, "Mr. Ratburn and the Special Someone", when one of the mainstay characters, Mr. Ratburn, not only came out as homosexual (marking the first instance of homosexuality in the series since the spinoff show Postcards from Buster), but also ended up entering a homosexual "marriage", with such an event being portrayed positively. The episode was skipped in Alabama and Arkansas.