A dumb Dora is 1920s American slang for a foolish woman.
The epithet arose from the vaudeville act of George Burns and his wife, Gracie Allen, It was eventually turned into a classic comic strip produced by King Features Syndicate. Although this strip was discontinued in 1935, a popular 1960s and 1970s CBS 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)