Alois Hitler was born Alois Schicklgruber in the hamlet of Strones, parish of Döllersheim, in the Waldviertel, an area in northwest Lower Austria, to a 42-year-old unmarried peasant, Maria Schicklgruber, whose family had lived in the area for generations. At his baptism in Döllersheim, the space for his father's name on the baptismal certificate was left blank and the priest wrote "illegitimate". His mother cared for Alois in a house she shared with her elderly father, Johannes Schicklgruber.
Sometime later, Johann Georg Hiedler moved in with the Schicklgrubers; he married Maria when Alois was five. By the age of 10, Alois had been sent to live with Hiedler's brother, Johann Nepomuk Hiedler, who owned a farm in the nearby village of Spital (part of Weitra). Alois attended elementary school, and took lessons in shoemaking from a local cobbler. At the age of 13 he left the farm in Spital and went to Vienna as an apprentice cobbler, working there for about five years. In response to a recruitment drive by the Austrian government offering employment in the civil service to people from rural areas, Alois joined the frontier guards (customs service) of the Austrian Finance Ministry in 1855 at the age of 18.
Historians have discussed candidates as Alois' biological father: Johann Georg Hiedler, his brother Johann Nepomuk Hiedler (or Hüttler), Leopold Frankenberger (whose existence has never been documented). During his lifetime, Johann Georg Hiedler was the stepfather and posthumously legally declared birth father of Alois. According to historian Frank McDonough, the most plausible theory is that Johann Georg Hiedler was the real father of Alois. An explanation for Alois being sent to live on his uncle's farm as a child is that Hiedler and Maria were simply too poor to raise him, or could not raise him as well as his uncle, or perhaps Maria's health was in decline.
Werner Maser suggests that Alois' father was Johann Nepomuk, Georg's brother and Hitler's step-uncle, who raised Alois through adolescence and later willed him a considerable portion of his life savings, but never admitted publicly to being his real father. According to Maser, Nepomuk was a married farmer who had an affair and then arranged to have his single brother Hiedler marry Alois' mother Maria to provide a cover for Nepomuk's desire to assist and care for Alois without upsetting his wife. This assumes Hiedler was willing to marry Maria in this situation, and Adolf Hitler biographer Joachim Fest thinks this is too contrived and unlikely to be true.
Alois' son Adolf, following the rumours that his paternal grandfather was a Jew, in 1931 ordered the SS (Schutzstaffel) to investigate the alleged rumours regarding his ancestry; they found no evidence of any Jewish ancestors. After the Nuremberg Laws came into effect within the Third Reich, Hitler then ordered the genealogist Rudolf Koppensteiner to publish a large illustrated genealogical tree showing his ancestry; this was published in the book Die Ahnentafel des Fuehrers (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 legitimised Johann Georg Hiedler as his father and the priest changed this on his birth certificate in 1876, this was considered certified proof for Hitler's ancestry; thus Hitler was considered a "pure" Aryan.