Ira Stadlen ( January 16 , 1924 -- April 18 , 2010 ) , known professionally as Allen Swift , was an American voice actor , known for playing characters including Simon Bar Sinister and Riff-Raff on the `` Underdog '' cartoon show .
Ira Stadlen ( January 16 , 1924 -- April 18 , 2010 ) or Allen Swift , was an American actor and painter . He is known for playing Simon Bar Sinister and Riff-Raff on the `` Underdog '' cartoon show .