General Sir William Thompson Adair KCB (21 June 1850 – 29 December 1931) was a Royal Marines officer and Ulster Unionist.

[2] Educated at Cheltenham College, he entered the Royal Marine Light Infantry as a lieutenant on 6 December 1867, and was promoted to captain on 1 July 1881.

In early February 1900 he embarked the SS Canada leaving Southampton for South Africa, where he was to serve in the Second Boer War.

[4] He received the brevet rank of colonel on 7 February 1900,[5] and was appointed Assistant Adjutant General on 1 November 1900.

Following his return to the United Kingdom, he was promoted colonel second commandant of the Royal Marine Light Infantry on 30 January 1902.