Who was Commander in Chief of the German army during World War 1?

The Chief of the Imperial General Staff was the top officer of the German Army. From 1906 through the first months of the war this was Helmuth von Moltke (The Younger). Helmuth von Moltke (The Elder) had been his uncle who was also a Chief of the Imperial General Staff who died in 1891. After the failure of the Schlieffen Plan to knock France out of the war in the first days, climaxed by the loss of the First Battle of the Marne, Moltke was replaced by Erich von Falkenheyn. Falkenheyn held the post until the failure of Verdun in 1916, coupled with reversals in the east, plus the incessant lobbying of von Hindenburg and Ludendorff, brought about his replacement by Hindenburg.

The real power in the German Army though, especially after 1916, was Erich Ludendorff. Ludendorff, who lacked the ennobling "von" in his name, indicating he was not by birth a member of the Prussian Junker class, became a virtual military dictator for about the last two years of the war, until the Kaiser surprisingly accepted his resignation about one month before the end. Ludendorff was always offering to resign if he did not get his way, and usually that threat was enough. Ludendorff was the Quartermaster General of the German Army, which position amounted to being the Deputy Chief of the Imperial General Staff, usually. But Ludendorff through the strength of his personality was able to dominate old Hindenburg as well as the Kaiser.

Paul von Hindenburg and Ludendorff were a team. Hindenburg had retired in 1912 as a Field Marshal, but was hastily called back in the first days of the war when the commander of the 8th Army, the sole field army left to face the Russians (while seven others were employed in the effort to knock out France) lost his nerve when the Russians unexpectedly lurched into motion much earlier than had been thought possible. Ludendorff, fresh from the reduction of the massive Belgian fortified city of Liege, was put aboard a train headed east, where he met Hindenburg for the first time. From that time on they operated together, first restoring the situation in the east, then moving to the Western Front. When decisions were necessary Hindenburg tended to dither and be irresolute, and after some time of that, Ludendorff would briskly inform all and sundry how things were going to be.