While commanders, as far back as we know the role, had personal companions and aides, a leader such as Alexander the Great would fight at the head of his troops, rather than commanding from a headquarters that let him see the the "big picture".
At some point in the eighteenth or nineteenth century, a recognizable staff function emerged. "In 1805, a new style of operational warfare burst upon the fields of Europe as Napoleon Bonaparte's Grand Army swept from the Rhine to the Danube surrounding the Austrian army at Ulm and initiating a revolution in military affairs (RMA) whose effects are still felt today. The question remains whether this new style of warfare was merely a natural outgrowth of the work of 18th century military thinkers, whose theories were imitated by a dynamic leader, or did Napoleon bring something new to warfare, a true innovation in the conduct of operational warfare?" Not all historians agree Napoleon was, indeed, that much of an innovator. 
Napoleon's transition to a staff model
Napoleon Bonaparte did not have a staff on the general model used by modern militaries, but was important in the transition between assistants to an individual and a modern staff. His Grand Quartier-General consisted of three main branches:
- Napoleon's Maison
- Grand Etat-Major General, headed by Marshal Louis Alexandre Berthier
The Maison was Napoleon's personal staff, but with an important addition to the usual clerks.
As opposed to the current role of an aide, which is both to relieve the commander of details, but also to learn how high commanders actually worked, Napoleon's aides were experienced general officers, each an expert in his own branch of service, who were 'trained up in Napoleon's own school of war', and capable of significant independent assignments, from a task force of all arms on the battlefield to the negotiating of a treaty.
In modern terms, these aides were a combination of high command observers, but also with delegated authority, even over Marshals of France, and the ability to command task forces. Napoleon had up to 12, although not all were present at every engagement. These officers had their own "little aides-de-camp, [who] were employed by Napoleon when needed."
This office was responsible for his correspondence and consisted of civilian secretaries, archivists, and a librarian.
Bureau de Renseignment
A military intelligence organization, responsible largely for strategic intelligence, which was passed on to Berthier's cabinet.
While this group did keep maps and plans, it was closer to the current intelligence and intelligence reference library of a modern intelligence staff. It kept Napoleon's situation map, but also reference materials on potential areas of operations and their resources.
Grand Etat-Major General
Napoleon's principal staff officer, Louis Alexandre Berthier, was trained by Pierrre de Bourcet. Kiley cites Spencer Wilkinson aptly stated, regarding Bourcet, that 'On every occasion when an important decision had to be made Bourcet would write a memorandum in which he analyzed the situation and set forth in detail, with full explanations and reasons, the course which seemed to him best. In very many cases, his suggestions were adopted and were usually justified by success, and when they were rejected the results were seldom fortunate.' Not only was Bourcet the most expert staff officer of his day, he was the first to come up with what is called today an estimate of the situation, as illustrated above. From him, and the staff school at Grenoble, of which he was the director from 1764-1771, came the embryo from which evolved the Napoleonic staff, of which Berthier was the preeminent product.'
A plan ought to have several branches ... One should ... mislead the enemy and make him imagine that the main effort is coming at some other part. And ... one must be ready to profit by a second or third branch of the plan without giving one’s enemy time to consider it. — Pierre de Bourcet
David Chandler maintains that "Napoleon contributed little new." As we struggle today with the implications of a possible RMA, it is important that we fully understand the forces that caused former RMA's to occur. For the historian, it is also important that we get our interpretations of past events as correct as possible. Was this a RMA that would have happened with any energetic leader who strictly followed the teachings of Bourcet and Guibert, as a sort of TTP put together by theorists, or did Napoleon take their theories, and meld them with his own ideas to create a new form of warfare and initiate a RMA? Does a true RMA require more than just theories and doctrine, does it require an inquiring mind on the part of the practitioner as well? 
For all the value Napoleon placed on key officers such as Berthier, Napoleon's staff was just that -- an organization built around him personally, rather than as a continuing entity. Recognizable staff organization, which split planning and supervisory functions into reasonably well-defined functions, usually are attributed to the Prussians, especially to Helmut von Moltke. Von Moltke did not invent the general staff, but created its modern shape.  Their earliest staffs did not follow the current model, but began with a military historian that would record how things were done in a given conflict, so officers could study and avoid mistakes of the past. Current staffs still have a historical function, which sometimes is formalized as a center for "lessons learned", as with Australia, Canada and the United States of America.
Moltke and mobilization
"...Helmuth von Moltke is the prototype model for modern operational leadership. In October of 1857, at the time of Moltke's accession to the position of Chief of the General Staff, Prussia alone retained a creative impulse and a potential for military innovation
"...provides a superb example in both his writings and in his actual application of the military arts. To understand Moltke's contribution, it is necessary to first understand the times in which he practiced his art. The Napoleonic era and its aftermath set the stage for Motlke's role in nineteenth century warfare.
"The events of the Napoleonic era resulted in a series of reforms in Prussia including the development of the General Staff system from which Moltke built an effective military machine. His mastery of planning, staff development, mobilization, deployment, sustainment, and the implementation of technology helped to make the Prussian (and later the German) army the master of Europe. He applied his talents, in conjunction with Chancellor Otto von Bismarck, to defeat Denmark in 1864, Austria in 1866 and France in 1870-71. Moltke was a student and admirer of Clausewitz, but did not follow all his prescriptions at all times. Moltke was a master of military efficiency and ranks among the great captains of all time. His greatness resulted primarily from superior management skills which he applied to military strategy and operations in a manner never surpassed before or since. Operational leadership, Operational art, Strategy levels of war, Planning, Sustainment, Moltke's contribution" 
When Moltke became head of the General Staff, he immediately made use of the high technology of the day, the railroad. In addition to Military History, he created a Lines of Communications department that dealt with railroad-based mobilization, operational movement, and logistics. Since use of railroads and the provision of logistics had to involve Prussia as a whole, he formed a civilian-military commission to operate the railroads in wartime.
Moltke was a keen judge of officer talent, selecting and training men of high ability, and distributing them throughout the army. General staff experience dominated even regular rank; the issue of an all-powerful "Great General Staff" was one of the reasons the U.S. National Security Act of 1947, which created the the U.S. Joint Staff, put a strict limit on the size of the Joint Staff.
In style, he believed that planning needed to be at a level of both artistry and technical perfection, but also recognized that micromanagement was inflexible. He implemented centralized control with decentralized operations, called
- Elevation of meticulous planning to the level of artistic perfection.
- Implementation of the concept of centralized control with decentralized execution of military operationsm a concept called Auftragstaktik, directive control, or mission-oriented orders.
- Keegan, John (1989), The Mask of Command, Penguin USA
- Wasson, James N. (21 May 1998), Innovator or Imitator: Napoleon's Operational Concepts and the Legacies of Bourcet and Guibert., School of Advanced Military Studies, U.S. Army Command and General Staff College, ADA357424
- Kiley, Kevin (January 2001), The Grand Quartier-General Imperial and the Corps d'Armée: Developments in the Military Art, 1795-1815
- Boyd, John R., Organic Design for Command and Control, Defense and the National Interest
- Goerlitz, Walter (1962), History of the German General Staff, 1657-1945, Praeger
- Australian Army, Welcome to the Centre for Army Lessons (CAL)
- Centre for Army Lessons Learned, Department of National Defence (Canada)
- Center for Army Lessons Learned, Combined Arms Center, United States Army
- Ohls, Gary J. (17 June 1994), The Operational Leadership of Helmuth von Moltke, U.S. Naval War College, ADA283481
- Keithly, David M. & Stephen P. Ferris (Autumn 1999, pp. 118-33.), "Auftragstaktik, or Directive Control, in Joint and Combined Operations", Parameters