Actually, it was his father who started using the name "Hitler." Nonetheless, as Adolf began his rise to power his opponents (while they still lived, that is) often called him "Schicklgruber" to mock him. Also, at least one historian has speculated that if Hitler's father hadn't changed his last name, history may well have turned out differently, as it's hard (so they claim) to imagine thousands of Germans shouting Heil Schicklgruber! in all seriousness.