Johanna Maria Bruhn was born in June 1926, the daughter of art historians in Berlin. She trained in medical technology before the outbreak of World War II, and after the war worked as a banker's secretary in Cologne. She started working for Herbert Quandt in Bad Homburg, near Frankfurt, in the mid-1950s, and eventually became his personal assistant. They married in 1960, shortly after increasing the family's stake in BMW to 50 percent in order to stave off a takeover attempt by Daimler-Benz.
The Quandt family's fortune was controversially amassed during the war. Herbert's father, Günther Quandt, was a top Nazi-era industrialist named by Adolf Hitler as a Wehrwirtschaftsführer – Leader of the Armament Economy. After Herbert's mother Antonie died, Günther remarried to Magda, a much younger woman. Following their subsequent divorce, Magda married Nazi master propagandist Joseph Goebbels (with Hitler as best man), and together raised Herbert's half-brother Harald.
A recent documentary found that the AFA, the company that the Quandts controlled during WWII, used slave labor provided by the Nazi regime to manufacture battery and munitions for the German war effort. Due to the subhuman living and working conditions, AFA lost approximately 80 forced laborers each month. Despite earlier denial of any wartime wrongdoing, the documentary and ensuing public attention prompted the Quandts to open their books to another investigation that confirmed their wartime activities.
The Quandts would later use the capital they amassed to buy BMW, of which they still hold 46.7 percent – the remaining 53.3 percent traded publicly. Following Herbert's death in 1982, Johanna took over 16.7 percent ownership in the company, with their son Stefan Quandt acquiring 17.4 percent and their daughter Susanne Klatten assuming 12.6 percent ownership. Stefan and Susanne, both members of BMW's supervisory board since 1997, are expected to inherit their mother's shares following her passing.
Johanna's personal fortune was estimated at nearly $14 billion. Though reclusive from media and public attention, she gave generously to charitable foundations that supported such causes as medical research and business journalism. She died in her home in Bad Homburg from undisclosed causes.