Harold Henry de Laessoe, Zimbabwean pioneer and administrator, was the son of A.F. de Laessoe, political resident in the Indian Civil Service. He was of Danish ancestry, born in Persia (now Iran), and educated in Denmark. In 1896, at the age of about 17, he came to South Africa and served in the British South Africa Police in Rhodesia (now Zimbabwe) until 1897. In December 1899 he was appointed as a clerk in the Native Department of Matabeleland, rising to Assistant Native Commissioner in May 1901, and Native Commissioner in July 1904. He was stationed in Bulawayo. His spare time was spent exploring and hunting in the territory that is now Zambia, and studying ethnology. He was a Fellow of the Royal Geographical Society, and in 1901 became a member of the Rhodesia Scientific Association.
In 1903 De Laessoe explored the Zambesi River from the Victoria Falls to the coast. His account of the journey, "The Zambesi River (Victoria Falls - Chinde); a boat journey of exploration, 1903", was published in the Proceedings of the Rhodesia Scientific Association in 1908 (Vol. 8(1), pp. 19-50). In 1905 he explored the Sabie River into Mozambique and wrote "The Lundi and Sabie Rivers" (Ibid, 1906, Vol. 6(2), pp. 118-138). [The Lundi, now the Runde River, joins the Sabi on the border between Zimbabwe and Mozambique].
In March 1908 he left the Native Department and in August that year was appointed manager of the British South Africa Company's estates, stationed in Bulawayo. Later he managed the ranches of the Liebig Company.