Ah, the ignoble name of Schicklgruber. Here's the story behind the name.
Adolf Hitler's paternal grandfather is a mystery; we have no idea who he was. His paternal grandmother was Maria Anna Schicklgruber, and she was not yet wed at the time of Hitler's father's birth.
Hitler's father was thus named Aloys Schicklgruber on his birth certificate. When Aloys was five years old, his mother married a man named Johann Georg Hiedler, who also adopted Aloys. At this time Aloys did not change his name. By the age of ten, he was sent off to live with his adoptive uncle, Johann Nepomuk Hiedler. Hiedler, for reasons unclear, chose to spell his surname 'Hitler'.
In his mid-thirties, Aloys did change his name. In 1876 he changed his last name to Hitler, after his uncle. He was apparently already going by Alois rather than Aloys at this time.
And so, when Alois Hitler had a (second) son in 1889, he named it Adolf Hitler rather than Adolf Schicklgruber. Alois and Adolf Hitler both claimed that Johann Hiedler was indeed their real, biological father/grandfather. This is possible, but highly disputed.
Political rivals revived the name Schicklgruber in order to mock Hitler, and Allied planes dropped "Heil Schicklgruber" propaganda leaflets over German cities. 'Schicklgruber' translates into "sump digger" in the German dialect used in the Waldviertel region of Austria.
Schicklgruber still pops up as 'Hitler's real name' from time to time, and even otherwise reputable sources will claim that Hitler was born Adolf Schicklgruber. This is rather silly, and baseless.