Erich Ludendorff was the most powerful German general at the end of the First World War, achieving practically dictator status from 1916 on.
Source: Lexikon Erster Weltkrieg
"Expected" here as most of the military officers were indeed members of the aristocracy and carrying a nobiliary particle in their names like the most frequent von or zu etc. His nominally senior partner in OHL leadership Paul von Hindenburg being just the next best example.
Ludendorff never had that von as part of his name. But he was born right into a family that had vast connections into the nobility. Quite a few members were indeed nobility.
Ludendorff was born on 9 April 1865 in Kruszewnia near Posen, Province of Posen, Kingdom of Prussia (now Poznań County, Poland), the third of six children of August Wilhelm Ludendorff (1833–1905). His father was descended from Pomeranian merchants who had achieved the prestigious status of Junker.
Erich's mother, Klara Jeanette Henriette von Tempelhoff (1840–1914), was the daughter of the noble but impoverished Friedrich August Napoleon von Tempelhoff (1804–1868) and his wife Jeannette Wilhelmine von Dziembowska (1816–1854), who came from a Germanized Polish landed family on the side of her father Stephan von Dziembowski (1779–1859). Through Dziembowski's wife Johanna Wilhelmine von Unruh (1793–1862), Erich was a remote descendant of the Counts of Dönhoff, the Dukes of Duchy of Liegnitz and Duchy of Brieg and the Marquesses and Electors of Brandenburg.
In a forum someone claims to be a family member and shares the detail that Kaiser Wilhelm II wanted to ennoble Ludendorff, invited him to an audience to discuss the proceedings, but Ludendorff is said to have declined the offer. (War Ludendorff adelig?)
The Encyclopaedia says:
Erich Ludendorff was born to be a soldier: Both his father and maternal grandfather had been officers in the Prussian cavalry. But Erich Ludendorff was not born to be a general. In Prussia (the dominant state in the cluster of Germanic states that would unify into the nation of Germany in 1871) generals came from the nobility. A person of noble birth was marked by the designation "von" before his last name. Ludendorff, born on April 9, 1865, was a commoner, raised in a struggling family that lived in the province of Posen. To reach the top of the German armed forces, he would have to work unrelentingly—and that is what he did.
This is confusing. Now, the von is not strictly necessary for being nobility, just incredibly "common" in those circles (excuse the pun).
Was he not nobility from birth? If not: why not, given the genealogy? Did he have the "title" of Junker, designating a very low rank within the nobility?