Which Prussian general served as Blücher's chief of staff during the 1815 campaign?

August von Gneisenau served as Blücher’s chief of staff during the 1815 campaign.

Gneisenau was a senior Prussian officer whose partnership with Field Marshal Gebhard Leberecht von Blücher combined Blücher’s aggressive battlefield leadership with Gneisenau’s staff work and operational planning. He had already served as Blücher’s chief of staff during the Wars of Liberation against Napoleon in 1813–1814.

When Napoleon returned from exile in 1815, Gneisenau again held the post in the Prussian Army of the Lower Rhine. He helped direct the campaign that culminated in the battles of Ligny and Waterloo. After Blücher was temporarily incapacitated at Ligny on 16 June, Gneisenau assumed command and ordered the army’s withdrawal toward Wavre rather than away from Wellington.

That decision enabled the Prussians to march to Wellington’s aid at Waterloo on 18 June. Carl von Clausewitz was also a notable Prussian military thinker and officer, but he was not Blücher’s chief of staff in the 1815 campaign. Friedrich von Bülow commanded a corps, not the army’s staff.