G.A.K. Marshall (known as Knox, later as Guy), a British entomologist, came of an Irish protestant family. His father, a keen naturalist, was a colonel in the Indian Army and later a judge in the Punjab. Marshall's interest in entomology was awakened early in his school days in England by a German master. He received his secondary schooling at Charterhouse School in Godalming, where his early interest in butterflies changed to beetles. After failing the Indian civil service examination at the age of 19 his father sent him to a sheep farm in Natal. By 1892 he had settled at Ennersdale, Natal, from where he presented a collection of Coleoptera (beetles) to the South African Museum in Cape Town, particularly tiny forms. The next year he moved to Salisbury (now Harare) in present Zimbabwe, where he worked in various government departments for two years. During this period he continued his donations of insects to the South African Museum - an extensive series representing various orders from Natal and Mashonaland in 1893, especially small species of Coleoptera, very well mounted, of which 160 were new to the museum's collections, followed by more insects from Mashonaland in 1894 and 1895. Upon leaving the civil service he went prospecting in Mashonaland, but continued collecting insects and birds.
Marshall's father provided him with capital to enter into a partnership to open a store in Harare under the name Bates and Marshall. He became co-manager of the Salisbury Building and Estates Company, and built the first double storey block for shops and offices in the town. While on a visit to Natal in 1897 he collected more Coleoptera for the South African Museum. He also met the young C.F.M. Swynnerton* and persuaded him to come to Harare, offering him a job in his store. His contributions to the South African Museum continued unabated: mammal and bird skins in 1898, and 172 species of Coleoptera and Hymenoptera the next year, about half of them new to the museum. As a result he was named as one of the museum's "correspondents" (of which there were only nine at the time), who received its publications free of charge. He presented further insects, and some other invertebrates, every year to 1905.
Five new genera and 21 new species of Coleoptera collected by him in Natal and Zimbabwe were described by H.S. Gorham in 1900. In the same year M. Jacoby described many new species of phytophagous Coleoptera collected by him and others. Some of his entomological observations were published in three papers by G. Lewis in 1897-1900, while A.G. Butler in 1898 published two papers on the Lepidoptera he had collected in Natal and Mashonaland during the previous few years. H. Wagner described his Apionidae (a sub-group of the weevils) in 1908.
Around 1900 Marshall bought Gungunyana Farm, close to the Portuguese border, which included part of the Mount Selinda forest. He later appointed Swynnerton to manage the farm, and eventually sold it to him. Marshall also owned two other farms.
Most of his ornithological activities were confined to the region around Harare. With the encouragement of Professor E.B. Poulton* of Oxford University he carried out research into the palatability of Lepidoptera to insectivorous birds. After brief "Notes on a small collection of birds from Mashonaland" (The Ibis, 1896) he published a fully annotated list, "Notes on Mashonaland birds" (1900) in the same journal. This paper, a list of 250 species, included notes on the stomach content of insectivorous birds and is one of the best faunal lists of its period for Zimbabwe.
Marshall's publications on the Lepidoptera, in British journals, included "Notes on seasonal dimorphism in South African Rhopalocera" (1896), "On the synonymy of the butterflies of the genus Teracolus" (1897), "Seasonal dimorphism in butterflies of the genus Precis" (1898), "Observations on mimicry in South African insects" (1900), and "Five years of observations and experiments (1896-1901) on the bionomics of South African insects" (1902). According to Poulton (1905) the latter comprehensive paper greatly enriched the subject of mimicry in insects; the most wonderfull example pertains to the flower-hunting beetles of the family Lycidae and the heterogeneous groups of insects that mimic their colouring. Marshall later contributed two further papers on mimicry (1907, 1909).
He returned to the United Kingdom in 1906 and received an appointment as curator of the Sarawak Museum on the island of Borneo (Malaysia). However, illness prevented him from leaving Britain and he did not take up the position. After recovering he was appointed to an entomological post in the Colonial Office in London. In 1909 he became scientific secretary to the Entomological Research Committee on Tropical Africa. The next year he founded and edited the Bulletin of Entomological Research, which contained summaries of papers of interest to economic entomologists. When the Imperial Bureau of Entomology (later the Commonwealth Institute of Entomology) was formed in 1913 he was appointed its first director and was responsible for founding its journal, the Review of Applied Entomology. He remained director until his retirement in 1942. During these years he developed into a renowned British entomologist.
After his return to England Marshall did only taxonomic research. He specialised in beetles of the huge weevil superfamily (Curculionoidea), on which he eventually published some 200 papers, describing about 2300 taxa over a period of almost 60 years. In 1907 he reviewed two of its groups, the Byrospinae and the genus Symthocus, in the Transactions of the South African Philosophical Society (Vol. 18). Some of the material he reported on was supplied by Albany Museum, Grahamstown. A major publication on this group was published as Volume 15 of The fauna of British India (1916). One of his later papers on this superfamily, "New South African Curculionidae (Coleoptera)" was published in the Annals and Magazine of Natural History (1955). He continued his studies at the British Museum to a few weeks before his death, at the age of 87, and his last papers were published posthumously.
Marshall became a member of the South African Philosophical Society in 1897 and continued his membership when it became the Royal Society of South Africa in 1908. By 1900 he had been elected a Fellow of both the Entomological Society of London and the Zoological Society of London, and over the years he refused the presidency of the former several times. He was a foundation member of the South African Ornithologists' Union (established in 1904) and served on its council from 1906 to 1909. He was also a member of the South African Association for the Advancement of Science from 1903 to 1906 and served on its council for 1903/4. In 1900 he was elected a life member of the Rhodesia Scientific Association, following his donation of 59 named species of butterflies and 53 named species of local birds to its museum in August that year. He joined the British Association for the Advancement of Science in 1905. In later years he was elected an honorary member of the South African Biological Society. He was elected a Fellow of the Royal Society of London in 1923.
Marshall's success as an entomologist is all the more remarkable because he had no formal education in science. The University of Oxford awarded him an honorary Doctor of Science (DSc) degree in 1915. In 1920 he was appointed a Companion of the Order of St Michael and St George (CMG) and upon his retirement advanced to Knight Commander of the same order (KCMG). He was married for the first time only in 1933, to Hilda M. Maxwell, the widow of J.J. Folliott, a distant relative with whom he had collected birds in Mashonaland in 1894. He was an able administrator, approachable, but of a retiring disposition. The genus Marshalliana of Goat Moths or Carpenter Moths and many insect species were named after him.