Lt Col Sir William Lennox Napier, 3rd Baronet of Merrion Square, (12 October 1867 – 13 August 1915), was a British baronet and soldier. He joined the Sussex Artillery Volunteers in 1888. He was commander of the 7th Battalion, Royal Welch Fusiliers, as part of the Territorial Army. He retired in 1912, but offered his services on the outbreak of the First World War in August 1914, and was commissioned as Major, 4th South Wales Borderers, on 24 September 1914 in command of "A" Company. He was married to Lady Mabel E. G. Napier (née Forster).