My mother, who was in her twenties during the Second World War, sometimes referred to Hitler as Schicklgruber, so I assume that this was a meme while we were at war with Hitler.
Here is some information on Hitler's granny, Maria Schicklgruber
Hitler's ancestry was questioned when his opponents began spreading rumours that his paternal grandfather was Jewish, since one of Nazism's major principles was that to be considered a pure "Aryan" one had to have a documented ancestry certificate (Ahnenpass).
In 1931, Hitler ordered the Schutzstaffel (SS) to investigate the alleged rumours regarding his ancestry; they found no evidence of any Jewish ancestors. He then ordered a genealogist by the name of Rudolf Koppensteiner to publish a large illustrated genealogical tree showing his ancestry. This was published in the book Die Ahnentafel des Führers ("The pedigree of the Leader") in 1937, which concluded that Hitler's family were all Austrian Germans with no Jewish ancestry and that Hitler had an unblemished "Aryan" pedigree. As Alois himself legitimized Johann Georg Hiedler as his biological father (with three witnesses affirming and watching this) and the priest changed the father's blank space on the birth certificate in 1876, this was considered certified proof for Hitler's ancestry, and thus Hitler was considered an "Aryan".
Some people disliked Hitler because he was a genocidal dictator. Others disliked him because they thought that they could run the Nazi party better, e.g. Otto Strasser, or they belonged to the Prussian military aristocracy and despised Hitler's class origins. The illegitimacy story, or the evidence-free claims that Hitler was Jewish, homosexual, or both, originated with Hitler's German opponents, even if the British and Americans disseminated them gleefully.