A dumb Dora is 1920s American slang for a foolish woman.
The epithet was popularized by the vaudeville act of George Burns and his wife, Gracie Allen, but was in use earlier. In 1924 it was turned into a comic strip drawn by Chic Young (of later Blondie fame) and produced by King Features Syndicate. Although this strip was discontinued in 1935, the TV game show Match Game occasionally alluded to the strip by asking those watching in the studio to shout in unison, "How dumb is she?" (borrowing from a routine from The Tonight Show). Flappers of the 1920s were also sometimes likened to dumb Doras.
Chic Young's Dumb Dora
(March 7, 1929)