Answer by taking a quote from the following article:

Ludendorff was born on 9 April 1865 in Kruszewnia near Posen, Province of Posen, Kingdom of Prussia (now Poznan 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 Donhoff, the Dukes of Duchy of Liegnitz and Duchy of Brieg and the Marquesses and Electors of Brandenburg.

In the West in 1916 the Germans attacked unsuccessfully at Verdun and soon were reeling under British and French blows along the Somme. Ludendorff's friends at OHL, led by Max Bauer, lobbied for him relentlessly. The balance was tipped when Romania entered the war, thrusting into Hungary. Falkenhayn was replaced as Chief of the General Staff by Field Marshal Hindenburg on 29 August 1916. Ludendorff was his chief of staff as first Quartermaster general, with the stipulation that he would have joint responsibility. He was promoted to General of the Infantry. Chancellor Bethmann-Hollweg warned the War Cabinet: "You don't know Ludendorff, who is only great at a time of success. If things go badly he loses his nerve." Their first concern was the sizable Romanian Army, so troops sent from the Western Front checked Romanian and Russian incursions into Hungary. Then Romania was invaded from the south by German, Austro-Hungarian, Bulgarian, and Ottoman troops commanded by August von Mackensen and from the north by a German and Austro-Hungarian army commanded by Falkenhayn. Bucharest fell in December 1916. According to Mackensen, Ludendorff's distant management consisted of "floods of telegrams, as superfluous as they were offensive."  When sure that the Romanians would be defeated OHL moved west, retaining the previous staff except for the operations officer, blamed for Verdun. They toured the Western Front meeting --and evaluating-- commanders, learning about their problems and soliciting their opinions. At each meeting Ludendorff did most of the commander's talking. There would be no further attacks at Verdun and the Somme would be defended by revised tactics that exposed fewer men to British shells. A new backup defensive line would be built, like the one they had constructed in the east. The Allies called the new fortifications the Hindenburg Line. The German goal was victory, which they defined as a Germany with extended borders that could be more easily defended in the next war.  Hindenburg was given titular command over all of the forces of the Central Powers. Ludendorff's hand was everywhere. Every day he was on the telephone with the staffs of their armies and the Army was deluged with "Ludendorff's paper barrage"  of orders, instructions and demands for information. His finger extended into every aspect of the German war effort. He issued the two daily communiques, and often met with the newspaper and newsreel reporters. Before long the public idolized him as their Army's brain.

What was their location?
Hindenburg was given titular command over all of the forces of the Central Powers. Ludendorff's hand was everywhere.