Lieutenant General Sir William Nicolay KCH CB (14 April 1771 – 3 May 1842) was a British Army officer present at the Battle of Waterloo who later became Governor of Mauritius.
He was the third son of Frederick de Nicolay, Principal Page to Princess Charlotte of Mecklenburg-Strelitz, wife of King George III.
He afterwards served under Sir Ralph Abercromby at Tobago and Trinidad until compelled to return home by a broken thigh, which incapacitated him for duty for two years.
He was employed on the defences of the Kent and Sussex coasts during the invasion alarms of 1804–1805, and on intelligence duties under Sir John Moore in Spain in 1808, and was present at Corunna.
He became a brevet colonel on 4 June 1813 and in 1815 proceeded to Belgium in command of five companies of the Royal Staff Corps, and was present at the Battle of Waterloo.