Theodore received his medical education at Aberdeen University, qualifying M.B. in 1898. He joined the Medical Services, at the rank of Lieutenant, on 27th June 1901, then saw active service in the South African War from 1901 to 1902, gaining the Queen’s South African Medal with 5 clasps, and was Mentioned in Despatches [L.G. 18th July 1902]. From 1903 to 1908 he served in India, during which time he gained promotion to Captain on 27th June 1904. from 1910 to 1911 he served in West Africa, then returned again in 1912 but was invalided. On 27th March 1913 he gained promotion to the rank of Major. After being mobilised for war on the 4th August 1914, Theodore joined the 1st Field Ambulance the next day, on the 5th, at Aldershot at 2 p.m. He entered the war with the unit on 18th August. The following day, on the 19th, the unit were in Boue. They visited a civil hospital in town but found no doctors there. Theodore, along with another officer and four nursing orderlies, took over charge of the hospital whilst the unit remained in the area. On 19th November he took over charge of the unit whilst the Commanding Officer, Lt Col Hinge, went on leave. He himself then took 96 hours leave when Lt Col Hinge returned on the 24th. On 6th January 1915 he was admitted into No 1 Clearing Hospital unwell. On the 9th he was sent down the line to the Base. From 10th July 1915 to 5th August 1919 Theodore served under the rank of temporary Lieutenant Colonel. He returned to active service becoming the Commanding Officer of the 47th Field Ambulance, remaining with them until 1917. He then served with No 20 Casualty Clearing Station from 1917 to 1919. After the war he served in Mesopotamia from 1919 - 1920. He then went onto reduced pay, and was granted the rank of Lieutenant Colonel on 18th August 1920. He ceased to be on the Roll of Officers from 16th June 1931. He was the son of Robert Ritchie.