The French VI Corps was held in reserve near La Belle Alliance at Waterloo.
Commanded by Georges Mouton, Count de Lobau, the corps initially stood in the second line near the centre of Napoleon’s position. It formed part of the force Napoleon could commit after the main attacks developed.
The reserve did not remain passive. As Prussian troops began arriving from the east, Napoleon moved Lobau’s corps toward Plancenoit, where it fought hard to protect the French right and the army’s line of retreat. This is why VI Corps is sometimes chiefly associated with the fighting around Plancenoit rather than with La Belle Alliance itself.
A common mix-up is to confuse the VI Corps with the Imperial Guard, which also formed a central reserve. The Guard was Napoleon’s elite final reserve, while VI Corps was a regular army corps that was redirected against the Prussians.