Butters Stotch, Pip Pirrup, and Wendy Testaburger are all characters in which long running animated TV series?

The answer is South Park as all four mentioned characters are part of the long-running animated TV series. Butters Stotch, Pip Pirrup, and Wendy Testaburger are frequent recurring characters on the show, known for their distinct personalities and storylines. South Park has been on the air since 1997 and is known for its satirical and often controversial humor, tackling a wide range of social and political issues through its characters and storylines.