Which French marshal served as Napoleon's Chief of Staff for most of his campaigns?

Louis-Alexandre Berthier served as Napoleon’s Chief of Staff for most of his campaigns. His formal role was chief of staff, or major general, of the Grande Armée.

Berthier began working with Napoleon during the Italian campaign of 1796, when Napoleon appointed him chief of staff of the Army of Italy. He excelled at turning Napoleon’s often rapid and complicated instructions into precise orders, schedules, maps, and reports. His administrative skill helped coordinate several corps operating far apart from one another.

Berthier remained with Napoleon through campaigns including Austerlitz in 1805, Jena and Auerstedt in 1806, Friedland in 1807, the 1809 war against Austria, and the invasion of Russia in 1812. He continued in the post until Napoleon’s first abdication in 1814. The common mix-up is to treat Berthier as Napoleon’s greatest battlefield commander; his strength was organization and staff work, not independent tactical leadership. Marshal Soult temporarily replaced him in 1815, but Napoleon missed Berthier’s efficiency before Waterloo.