Ludovic "Sandy" Gustavus Arbuthnot, later 16th Lord Clanroyden is a fictional character who appears in various books by John Buchan in the Richard Hannay series. These books include Greenmantle, The Three Hostages, The Courts of the Morning, and The Island of Sheep, but not the first in the series, The Thirty-Nine Steps. He also appears in The League of Heroes by Xavier Mauméjean. His particular expertise is in adopting disguises which completely take in Hannay, the "friend [he] knows best in the world".