South African horticulturalist from Pretoria. David Spencer Hardy began his career in 1951 as a technician at the Veterinary Research Institute in Onderstepoort, but from 1958 until his retirement in 1991 he was a horticulturalist at the Pretoria National Botanical Garden, where he was responsible for cultivating the collected material brought in by staff scientists and other plant collectors. He collected extensively across Northern Cape Province, and made expeditions to the Northern Province, Namibia, Angola, Madagascar, Mauritius, and the Comoro Islands. His collections, which included living material and more than 7,000 specimens, were the basis of many of the plates published in The Flowering Plants of Africa during the period of his employment at NBG.

In the nursery, he set aside two greenhouses for his pet projects: rare and endangered Madagascan plants and plants of the Namib Desert. His main passion was the succulents, which he sought to popularise in more than 100 articles in the semi-popular press, at public talks, and over the radio. As well as being co-author of two books on succulents, Aloes of the South African Veld (1972) and Succulents of the Transvaal (1992), he wrote up a small portion of his collected material in the Flowering Plants of Africa and contributed to articles in scientific journals, including descriptions of at least seven new taxa.

After his retirement, he volunteered in Madagascar. He helped revive the Jardin Botanique et Zoologique de Tananarive, participated on a survey of aquatic weeds in the Antananarivo area, and contributed to the restoration of the spectacular Aloe suzannae Decary. He was a member of botanical societies in South Africa, Britain, the United States of America and Mauritius and was honoured in his lifetime by the South African Association of Botanists and the Cactus and Succulent Society of America. Several plant species are named after him: Stultitia hardyi R.A. Dyer, Stapelianthus hardyi Lavranos, Aloe hardyi Glen, Cyphostemma hardyi Retief, and Strumaria hardyana D.Müll.-Doblies & U.Müll.-Doblies. However, the first dedication he received was for the blood-sucking fly, Raymondia hardyi Fiedler, which he discovered on a bat as a teenager.