Roman Sandgruber's book Hitler's Father, as its title suggests, purports to be the first dedicated biography of Alois Hitler (né Schicklgruber), but we all know whose spectre dominates the pages. The book continues for a number of chapters after Alois' death, covering the death of Klara, Adolf's mother, and the young Adolf's development as a teenager. The book can more accurately be described as another history of the young Adolf Hitler, delving as deep as his grandparents' generation as books on the young Hitler often do.
Sandgruber's selling point, as the book's subtitle Hidden Letters suggests, is the recent discovery of a cache of Alois Hitler's letters in an attic, and Sandgruber's analysis of these is incorporated into his biography/history. In truth, these are of limited academic value, being mostly business correspondence with little revealed of Alois' personality or family matters. They are further shafts of light onto a part of history that remains partly shrouded in mystery (in no small part due to the Nazis' successful erasure of much of the evidence of Hitler's family record during his time in power) but they're also no more than colour to the already-known facts of young Hitler. For its part, Sandgruber's book is one of the more comprehensive accounts on this topic that I've come across, and would be recommended even if it did not have those letters from Alois (some of which are reproduced in their entirety, somewhat unnecessarily).
Where Sandgruber's book was less successful was with its thesis. As the book's sub-subtitle, Why the Son Became a Dictator, suggests, Sandgruber argues that the events and influences of Hitler's youth substantially contributed to the evil dictator he later became, the "important key" for understanding the Führer's mind (pg. 4). But the argument itself is made only sporadically in Sandgruber's book, and with all due respect to the author's academic integrity may well have been an angle by which to garner the book attention and sales than a genuine argument. While everyone's youth influences the adult they become, I was less convinced by this than by the thesis of Bradley F. Smith's 1967 book on Hitler's youth, which argues the later years of Vienna and World War One made the Hitler who dragged the world into hell, rather than any influence of Alois or Klara. While Sandgruber does make some good points, not least the disturbing foreshadowing of the later Final Solution in the discussion among early 1900s German ethno-nationalists about 'the Jewish question' and the idea that gypsies should be marked with tattooed numbers (pp227-8), it is an unemphatic thesis.
In light of this, Sandgruber's book can be highly recommended on the topic of Hitler's youth pre-Vienna, gathering as it does a sizeable amount of up-to-date primary research and providing a comprehensive approach to presenting it. But it will not be the last word on the subject.