Sweet Polly Purebred is the love interest of Underdog. She is a soft parody of Lois Lane as Underdog is a soft parody of Superman. She is a dog news reporter and gets kidnapped in most episodes. When she gets kidnapped by a villain, she starts singing, "Oh where oh where has my Underdog gone" in a whiny voice, hoping for him to come and save her. Her song often annoys villain Simon Bar Sinister. Underdog always comes to the rescue for her, and defeats the villain.
Polly bears a resemblance to Underdog, except with platinum blonde hair and her outfit is similar to a female news reporter's outfit. She loves Underdog, and he loves her.Polly also appeared in the 2007 live-action Underdog movie, where she is voiced by Amy Adams and is owned by a girl named Molly. She serves as the primary love interest for Underdog.