Friedrich Karl Freiherr von Eberstein (14 January 1894 – 10 February 1979) was a member of the German nobility, early member of the Nazi Party, the SA, and the SS (introducing Reinhard Heydrich to Heinrich Himmler in July 1931). Further, he rose to become a Reichstag delegate, an HSSPF and SS-Oberabschnitt Führer (chief of the Munich Police in World War II), and was a witness at the Nuremberg Trials.
Eberstein was born on 14 January 1894 in Halle on the Saale, of the Dillenburger branch of the von Eberstein family. His father was an army major. Karl was at cadet schools until 1912. Early on in World War I, Karl served in the German Army with Field Artillery Regiment 17 in August 1914. He was also a balloon observer, and later a battery commander in Artillery Regiment 16. He was awarded the Iron Cross Second Class and the Iron Cross First Class. After World War I, Eberstein fought as a member of the Freikorps in Middle Germany and/or Upper Silesia, and also with the Halle "Protection Police". After that, he went into banking.
Eberstein joined the (NSDAP) Nazi Party in 1922, but quit after the Beer Hall Putsch in November 1923. He then re-joined the Party in 1925 with number: 15067. He was an early member of the SS (membership number: 1386) and on the staff of Heinrich Himmler. According to Jonathan Petropolous, Eberstein was part of Himmler's strategy to attract members of the nobility and aristocracy to the SS. Eberstein obtained the officer rank SS-Sturmführer on 1 April 1929. He also joined the SA in July 1930 but left it later.