Louis Thomas Gunnis Leonowens (25 October 1856 – 17 February 1919) was a British subject who grew up and worked in Siam (Thailand). He was the son of Anna Leonowens, famous as a tutor of King Mongkut. Leonowens later served as an officer with the Siamese Royal Cavalry and founded a Thai trading company that still bears his name, Louis T. Leonowens Ltd. He was the basis of a major character in the 1944 novel Anna and the King of Siam, as well as other fictional works based on it.