The rank of Grand General had only been found in use by the Galactic Empire. Grand General was a powerful and highly influential rank in the Imperial hierarchy, and was outranked only by the Imperial Exeutor/Supreme Commander, Grand Vizier, the Emperor, and the Emperor's numerous lieutenants and Dark Side Elite. The rank was equivalent to Grand Admiral, its Imperial Navy counterpart, but the rank of Grand General had not quite gained the galactic reputation that Grand Admiral had over the years.
During the reign of Palpatine, there were originally twelve Grand Generals whom collectively were known as the Grand General's Council. One such Grand General served as a superior, known as the Chief Army Officer, or the Chief of Army Operations, who served as the chief administrator of the Imperial Army. The Council and the Chief Naval Officer reported directly to the Imperial Military's Commander-in-Chief, the Military Executor/Supreme Commander, who, at Palpatine's time, was none-other than the Dark Lord of the Sith and Palpatine's lieutenant, Darth Vader.
Many of the original Grand Generals were responsible for the devastation caused during the Post-Endor Imperial power struggle. Taking complete control over resources at their disposal and elsewhere, these Grand Generals carved out their own spheres of influence and warred amongst each others and against the Navy as Warlords.
By 8 ABY, all the original Grand Generals had either been killed during the Civil War or assassinated by agents of Bacharan Valak. Once Valak achieved the goal of an Imperial re-unification and was coronated Emperor, he set out to revive the Grand General's Council and restore the Empire and the Imperial Army to its former glory.
Grand Generals were appointed by the Emperor and the Emperor alone, and answered directly to the Executor (or in certain cases in whcih the Executor could not be reached, the Emperor), in all matters. The creation of the rank of Grand General two years before the Battle of Yavin was widely recognized as a means to increase the Emperor's direct control of the Imperial Military. However, although all exceptionally gifted officers, the Grand Generals were not just front-line commanders; rather, they included several technical specialists and theoreticians, enabling them to serve as a leadership cadre for the whole military—and indeed the whole Empire.
All Grand Generals, upon promotion to the rank, were also given the esteemed and unique position in the Empire known as Warlord, a post held only by a few of the Emperor's most gifted military commanders. This, however, was done away with by Valak, and only Valak's personal and elite military commanders were given the post, such as Jarl Rellik, regardless of their military rank.
Unlike Grand Admirals, the Grand Generals did not wear the distinguishable white uniform. Instead, they were the familiar olive-gray uniform of any other Imperial military officer.
Grand Generals did not have authority in the Stormtrooper Corps.