Born in the Austrian village of Spital, Weitra, Waldviertel, her father was Johann Baptist Pölzl and her mother was Johanna Hiedler. Either Johanna Hiedler's father Johann Nepomuk Hiedler or his brother Johann Georg Hiedler (who is presumed and accepted as the father) was the biological father of Klara Hiedler's husband, Alois Hitler, Sr.. Therefore, Klara and Alois were most likely first cousins once removed.
In 1876, three years after Alois Hitler's first marriage to Anna Glasl-Hörer, Alois hired 16-year-old Klara as a household servant. After the death of his second wife — Franziska Matzelsberger — in 1884, Alois and Klara began seeing each other, and were married on 7 January 1885 in a brief ceremony held early that morning at Hitler's rented rooms on the top floor of the Pommer Inn in Braunau. Alois then went to work for the day at his job as a customs official. Their first son — Gustav — was born four months later, on 15 May 1885. Ida followed on 23 September 1886. Both infants died ofdiphtheria during the winter of 1886-1887. A third child, Otto, was born and died in 1887.
Adolf was born 20 April 1889, followed by Edmund on 24 March 1894 and Paula on 21 January 1896. Edmund died ofmeasles on 28 February 1900, at the age of five. Klara's adult life was spent keeping house and raising children, for which, according to Smith, Alois had little understanding or interest.
Alois and Klara's children were:
- Gustav Hitler (born 10 May 1885, died of diphtheria on 8 December 1887 in Braunau am Inn)
- Ida Hitler (born 23 September 1886, died of diphtheria 2 January 1888 in Braunau am Inn)
- Otto Hitler (born and died 1887 in Vienna, lived three days)
- Adolf Hitler (born 20 April 1889, committed suicide 30 April 1945), German dictator
- Edmund Hitler (born 24 March 1894, Passau, died of measles, 28 February 1900, Leonding)
- Paula Hitler (born 21 January 1896, died 1 June 1960), the last surviving member of Hitler's immediate family.
Klara Hitler first discovered a lump in her breast in 1905 but initially ignored it. After experiencing chest pains that were keeping her awake at night, Klara finally consulted the family doctor, Eduard Bloch, in January 1907. Bloch chose not to inform Klara that she hadbreast cancer and left it to her son Adolf to inform her. Dr. Bloch told Adolf that Klara had a small chance of surviving and recommended that she undergo a radical mastectomy. The Hitlers were devastated by the news. According to Dr. Bloch, Klara "accepted the verdict as I was sure she would - with fortitude. Deeply religious, she assumed that her fate was God's will. It would never occur to her to complain." Klara underwent the mastectomy at Sisters of St. Mercy in Linz whereupon the surgeon, Dr. Karl Urban, discovered that the cancer had already metastasized to the pleural tissue in her chest. Bloch informed Klara's children that her condition was terminal. Adolf, who had been in Vienna ostensibly to study art, moved back home to tend to his mother, as did his siblings. By October, Klara's condition had rapidly declined and Adolf begged Bloch to try a new treatment. For the next 46 days (from November to early December), Bloch performed daily treatments of iodoform, a then experimental form of chemotherapy. Klara's mastectomy incisions were reopened and massive doses of iodoform soaked gauze was applied directly to the tissue to "burn" the cancer cells. The treatments were incredibly painful and caused Klara's throat to paralyze, leaving her unable to swallow. The treatments proved to be futile and Klara died at home in Linz from the toxic medical side-effects on 21 December 1907. Owing to their mother's pension and money from her modest estate, the two siblings were left with some financial support. Klara was buried in Leonding near Linz.
Adolf Hitler, who had a close relationship with his mother, was devastated by her death and carried the grief for the rest of his life. Bloch later recalled that "In all my career, I have never seen anyone so prostrate with grief as Adolf Hitler." In his autobiography Mein Kampf, Hitler wrote that he had "...honored my father, but loved my mother" and said that his mother's death was a "dreadful blow...." Decades later, in 1940, Hitler showed gratitude to Bloch (who was Jewish) by allowing him to emigrate with his wife from Austria to the United States.
On 28 March 2012, the tombstone marking Alois Hitler's grave (and that of his wife, Klara) in Town Cemetery in Leonding was removed, without ceremony, by a descendant, according to Kurt Pittertschatscher, the pastor of the parish. The descendant is said to be an elderly female relative of Alois Hitler's first wife, Anna, who has also given up any rights to the rented burial plot. The plot was covered in white gravel and left with its distinguishing single tree which has since been removed, but the grave is very easy to locate. The remains of Hitler's parents are still interred in the grave.