Rear-Admiral Sir Robert Keith Arbuthnot, 4th Baronet, KCB MVO (23 March 1864 – 31 May 1916) was an automotive pioneer and a British Royal Navy officer during World War I. He was killed at the Battle of Jutland, when the cruiser squadron he commanded came under heavy fire after a bold but ill-judged attack on the German battle fleet.
Born in Alderminster to Major Sir William Arbuthnot, 3rd Baronet and Alice Margaret Thompson, he succeeded to his father's baronetcy on 5 June 1889. In 1904, he became a Member of the Royal Victorian Order (MVO).
He had a Sunbeam Tonneau and competed with it in the 1904 Bexhill Speed Trials. An enthusiastic member of the Motor Cycling Club, he kept his motorbike in his day cabin and engaged in long distance endurance races.
1908 Came third in the single-cylinder class of the Isle of Man TT, and an annual rally in the Isle of Man and a TT trophy for service members are named after him. He had been a member of the M.C.C. since 1898, and had played for the Club, United Services, and the Navy. There is also a hamlet and post office named after him in Saskatchewan.
He was married on 11 December 1897, to Lina MacLeay (1868–1935), daughter of Colonel Alexander Caldcleugh MacLeay. They had one daughter.