Archibald Algernon Henry St. Maur, formerly Seymour, 13th Duke of Somerset, etc. (30 December 1810 – 28 Berkeley Square, London, Oct 1891) was the son of Edward St. Maur, 11th Duke of Somerset and Lady Charlotte Douglas-Hamilton. He was also a baronet. His motto, Foy Pour Devoir, "Faith for Duty", has been adopted by HMS Somerset (IV) by permission. Archibald died at the age of 80, unmarried and childless, was interred at Maiden Bradley, Warminster, Wiltshire, and his titles passed to his brother, Algernon St. Maur.