Riff Raff is a villain in which American cartoon?

Underdog is an American animated television series that ran from October 1964, to March 1967. The show continued in syndication until 1973.

Underdog, an anthropomorphic dog who is 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 actor Wally Cox (December 6, 1924 – February 15, 1973).

When villains threatened, Shoeshine Boy ducked into a telephone booth, where he transformed into the caped and costumed superhero, destroying the booth in the process when his superpowers were activated. The villains almost always managed to menace Sweet Polly Purebred an anthropomorphic canine TV reporter, as part of their nefarious schemes.

Recurring villains included Riff Raff, voiced by Allen Swift (January 16, 1924 – April 18, 2010), an anthropomorphic wolf gangster based on noted actor George Raft.

Most episodes used a common template as the final scene. A crowd of people looking up into the sky would say, "Look in the sky!" "It's a plane!" "It's a bird!" Then a woman exclaimed, "It's a frog!" Another onlooker would respond, "A frog?" To this, Underdog replied with these words: "Not plane, nor bird, nor even frog,

It's just little old me, (at this point, Underdog would crash into something, then sheepishly finish), "Heh-heh-heh. Underdog."