What female dog is the secret object of US cartoon character Underdog's affections?

"Underdog" is an American animated television series that debuted October 3, 1964, on the NBC network under the primary sponsorship of General Mills, and continued in syndication until 1973 (although production of new episodes ceased in 1967), for a run of 124 episodes.

Underdog, Shoeshine Boy's heroic alter ego, appears whenever love interest Sweet Polly Purebred is being victimized by such villains as Simon Bar Sinister or Riff Raff. Underdog nearly always speaks in rhyming couplets, as in "There's no need to fear, Underdog is here!" His voice was supplied by Wally Cox. The villains almost always managed to menace Sweet Polly Purebred (voiced by Norma MacMillan), an anthropomorphic canine TV reporter, as part of their nefarious schemes; she was a helpless damsel in distress most of the time and had a habit of singing in a somewhat whining tone of voice, "Oh where, oh where has my Underdog gone?" This she would sing, to the music of the song "Oh Where Has My Little Dog Gone", whenever in jeopardy.