Ivar Thord-Gray (sometimes Gray, Ivar Thord) was originally named Hallstrom, but changed his name when he joined the British military in 1896. He went to sea at the age of 17, came to South Africa and worked for a farmer. When the war with the Matabele broke out in present Zimbabwe in 1896 he joined the British Army. From 1897 to 1902 he served in the Cape Mounted Rifles, attaining the rank of lieutenant. After the Anglo-Boer War (1899-1902) he was a cavalry captain during the Bambatha rebellion in 1906. Later in 1906 he was sent to East Africa where he became an instructor and inspector for the British police.
Thord-Gray published "Notes on the geology of the Lydenburg goldfields" in the Transactions of the Geological Society of South Africa (Vol. 8, pp. 66-81) in 1905. He was a member of the society, and of the South African Association for the Advancement of Science, in 1906. Around this time he participated in the discussion of a paper by G.G. Holmes* on "The Pretoria Series in the Marico District". The discussion was published in 1907.
As a professional soldier Thord-Gray fought on the side of the United States in the Filipino war of 1907-1908, with the French in Cochin China, with the Italians in Lybia (1911), with the Chinese army in the 1913 revolution, on the revolutionary side in Mexico, and with the British in World War I (1914-1918). From 1925 he lived in the United States and became an American citizen in 1931. He wrote Attack and defense in trench warfare (London, 1917) and a book in Swedish on Mexican temple ruins in 1923.