Short answers, pulled from the story.
Adolf Hitler established the Oberkommando des Heeres in 1935 as a central pillar of his rearmament program. This new command structure replaced older military hierarchies that had been restricted by international treaties.
Field marshal Walther von Brauchitsch held the title of Commander-in-chief of the Army before his removal following the Battle of Moscow. His dismissal occurred partly due to failing health and partly because of the disastrous outcome in December 1941.
Hitler limited the OKH authority to the Russian front after the Moscow crisis while granting the OKW direct authority over army units elsewhere. This arrangement created a jurisdictional rivalry between two organizations headquartered within the same Maybach complex in Nazi Germany.
In 1944, Friedrich Fromm served as C.-in-C. Reserve Army and Chief of Equipment within the OKH hierarchy. Rudolf Schmundt held the position of Chief of Army Personnel Office during this period while Heinz Guderian acted as Inspector General of Armoured Troops.
The unit operated independently until February 1938 when political changes altered its status within the state apparatus. Its creation signaled a decisive break from previous constraints and marked the beginning of open military expansion.