Harold St George Gray was one of only two people, apart from the General himself, associated with both Pitt-Rivers' private museum in Farnham, Dorset and with the Pitt Rivers Museum, at the University of Oxford.  The Somerset Archaeological and Natural History Society's own website says of him:
No individual achieved more for the society than the able and combative Harold St George Gray
Harold was born on 15 January 1872 in the Close at Lichfield. There is no record of his education but most of the sources say he received 'his scientific training with General Pitt-Rivers'. [Who Was Who]
Harold and his brother Claude started worked with Pitt-Rivers in 1888. Harold took over Frederick James's position as the General's secretary and Bowden suggests that he stayed until Pitt-Rivers' death in May 1900. [1991: 106]  His elder brother Claude left in 1892, according to Bowden 'after a quarrel with Pitt-Rivers', and emigrated to Canada.
Harold took part in the excavations that Pitt-Rivers carried out on his own estate. In 1893 Harold helped supervise the excavations at Handley Hill with Charles Flower and Herbert Toms. In 1897 he was in charge of the Iwerne site with G. Waldo Johnson.
Gray also helped Pitt-Rivers acquire objects from his collection, he had:
'with my old chief had much experience in buying in the London sale-rooms and elsewhere. By arrangement, on some occasions, the General and myself and a friendly dealer were apparently bidding against one another and opposing at times Sir Wollaston Franks [sic] and Sir Hercules Read, who were buying for the British Museum, and Canon Greenwell; these, I can assure you, were exciting times.' [Bowden, 1991: 144 quoting from the Gray papers]
In 1899 he left Pitt-Rivers' employment (possibly as a result of Pitt-Rivers' increasing ill-health and associated diminishment of activity) and began work at the Pitt Rivers Museum at Oxford where he was chief museum assistant to Henry Balfour, the Curator. In 1899 he also married Florence Harriet Young. The Museum's annual reports state:
... The incoming assistant, H. St. G. Gray, had been employed for some ten years by General Pitt-Rivers, and had received an invaluable Archaeological and Museum training under that most careful and systematic of observers. [1898-1899]
Considerable progress was effected during the year 1900 in the work upon the existing collections and upon the new material acquired by donation and purchase. In this work I have been very ably supported by Mr. H. St. G. Gray, whose skilled assistance has been most valuable, the Museum having greatly benefited thereby.
In March the Curator lost the services of Mr Gray, who left in order to take up an appointment as Curator of the Museum at Taunton. The work has been greatly hampered in consequence, as Mr Gray had rendered valuable service during the period in which he acted as assistant.The post has not yet been filled up, partly because of the difficulty of doing so adequately, and partly because the money was required for the purchase of exhibition cases which were very urgently needed, and the only way in which these could be procured was by assigning to this purpose the greater part of the money usually spent in wages. A fair amount of general progress in the Museum has, nevertheless, been effected. 
He gave several objects to the Pitt Rivers Museum. One was given presumably shortly after he arrived in Oxford, a small musical bow from Gabon, Africa which he had obtained at the Wharton collection sale in 1899 [1899.63.1]. Pitt-Rivers also obtained items from this collection, but his were obtained from a dealer George Fabian Lawrence. It is clear that when Gray moved from working with the first Pitt-Rivers collection to the second, he brought parts or the influence of the original with him. One of his first donations [to the Pitt Rivers Museum] was a hazel root which grown round a piece of flint, found on Cranborne Chase near Rushmore. [1899. 63.2]
Other objects given at around the same time, also record his continuing connections to the area; a hand-loom shuttle, netting needle and iron beater formerly used in the Wilton carpet factory for making Axminster carpets and given through him. [1899.49.1-3] Another object was a string of coral beads from Benin, 1900.32.4, donated whilst he was working there. As Pitt-Rivers' is one of the most famous collectors of Benin material it is perhaps something he acquired during his time working for the General, when he must have attended the auctions where most of the Benin material was sold. Other objects given in September 1900 before he left, were an 'old penknife with a bone or ivory handle, ploughed up in Motcombe, north Dorset' which he gave in September, it is not clear how he acquired it [1900.32.1]; a bronze surgical instrument or ear-cleaner, found with Roman remains in London [1900.32.2]; one of the medallets which Pitt-Rivers used to place in the foot of a trench to mark his excavation [1900.32.3] (there are further examples given by the Pitt-Rivers family to the museum).
He also continued to give objects after he left:
1901.70.1-2 These objects were loaned to the Pitt Rivers Museum and were two casts of socketed bronze celts taken from a mould of syenite found at Bulford, near Amesbury, Wiltshire. The two moulds are on opposite sides of the stone. These are Add.9455vol3_p1173 /1 and Add.9455vol4_p1316 /1-2 from the Cambridge University Library catalogue of Pitt-Rivers second collection.
1902.28.1 Mounted photograph of 'Hispano-Moresque' lustre dish ("Febershaun dish") showing a modified floral loop-coil form, circa 16th century. (This item shows the on-going influence of Pitt-Rivers in its interest in the decorative form)
1902.28.2 Piece of undyed barkcloth from Uganda which was found unentered in the accession book at the time but was donated in 1902. Again, it is not known how or where he obtained it.
1903.28.1 Photograph of two hearts stuck with pins in Taunton Museum. Gray will have known that the Pitt Rivers Museum had similar objects. A much more detailed catalogue card records this object as:
Amulets A Signatures B Sym(pathetic) Magic C Div(ination) and Witchcraft - B Sympathetic Magic - B.5 Black Magic - Figure Symbols (cords &c) - Description: Two drawings [on one card] of specimens [insert] of animals' hearts stuck with pins & thorns [end insert] in Taunton Castle Museum.:- 1. Heart stuck with pins & thorns, found Oct. 1882 in recess up a chimney in Mr. Cottrell's house, Ashbrittle. It was wrapped in a flannel bag. There was an old custom, when a pig died from supposed "over looking" by a which, of sticking pins and white-thorns into its heart, which was placed up the chimney. As long as it lasted, no witch would have power over the [continues on reverse of card] owner's pigs. 2. Heart stuck with nail and pins. The pinheads form the initials M.D., probably those of the supposed witch. Found nailed up inside the beam or "clavel" of a fireplace in an old house at Staplegrove, Taunton, in 1890. [insert] NC GC Rt (side of case). [end insert] Locality: Somerset. How Acquired: drawings presented by H. St. George Gray, Taunton Museum 1903. References: Elworthy, Evil Eye : 53, 54.
1905.2.1 'H. ST. G. GRAY Esq., The Museum, Taunton, Somerset. March - Rare carving of an animal in wood, used as a domestic idol, Easter Island, S. Pacific. This was bought by Mr Gray at a small sale in Taunton in 1904.'
1905.2.2 Lead cast of double looped palstave from Somersetshire. It is clear from research by Matt Nicholas as part of the Characterizing World Archaeology Collections at the PRM that the original axe [of which this is a copy] was found in the civil parish of West Buckland [ST 161 225] in the district of Taunton Deane. The axe formed part of a Bronze Age hoard discovered whilst digging a drain. The hoard is recorded on the English Heritage-maintained National Monuments Record under monument no. 189298. According to the NMR record the original objects whereabouts of the hoard [formerly in the W.A. Sandford collection] is unknown "but a set of plaster casts were made circa 1884 and are in the Pitt-River Museum, Oxford". The NMR record can be accessed online here.
1908.15.1 Brass thimble, probably medieval, dug up two feet down in cultivated land at Beckhampton, Wiltshire.
1912.41.1-2 2 leg bones of sheep (broken) which were perforated at one end and possibly used as weaving bobbins, from his excavations at the Glastonbury lake village. The site was excavated by Glastonbury Antiquarian Society between 1892 and 1908.
He remained at Oxford for two years until he resigned in 1901 to become assistant secretary, and librarian-curator of the museum for the Somerset Archaeological and Natural History Society in Taunton, where he remained until 1949.
Harold was one of the few staff who worked for Pitt-Rivers who continued to work in archaeology after his death. He carried out several very important excavations at Avebury, Maumbury Rings and lake villages in Glastonbury and Meare. Unfortunately he did not publish his findings and Bowden suggests that his archaeological methodology would not keep up with contemporary practises. [1991: 164-5] His Who Was Who entry (presumably at least contributed to personally) says:
Formerly Director of archaeological excavations for the British Association and other Societies and Committees. ... Keeper of the Somerset County Museum, 1901-1949; Pres. South-Western Naturalists’ Union, 1945-1947.
Excavations at Arbor Low Stone Circle, Derbyshire, 1903; Memoir of General Pitt-Rivers, DCL, FRS, and Index to his Works, 1905; The Stone Circles of East Cornwall, 1908; Excavations at Wick Barrow, Somerset, 1908; Reports on the Meare Lake Village, Ham Hill (Som.), Maumbury Rings, Kingsdown Camp. Battlegore (Williton), Warham Camp (Norfolk), Combe Beacon (nr Chard), and Burrow Mump (Som.), 1908-1939; The Yeovil Gold Torc, 1909; The Avebury Excavations, 1908-1922, 1934; joint author of The Glastonbury Lake Village, vol. i 1911, vol. ii 1917, and of The Meare Lake Village, vol. i 1948, vol. ii 1953; author of numerous papers in various transactions on archaeological excavations in England.
Gray had responsibility for taking care of the Society's collections and their public displays. He established the Wyndham gallery there in 1934 and acquired many new objects for the collections. His wife contributed to this, making sure that the collections were well documented.
He was president of the Somerset Archaeological and Natural History Society in 1951-2. He was described on the Society website as 'a pivotal character in the history of Somerset Archaeology and the Society'. Gray died on 28 February 1963. His correspondence and reports are held at Somerset Heritage Centre and the Alexander Keiller Museum.
See here for his account of being one of Pitt-Rivers' assistant
 The other was Leonard Halford Dudley Buxton who worked with the staff from the Pitt Rivers Museum during his time at the Oxford University Museum and in Farnham around 1929.
 This, however, is contradicted by the Pitt Rivers Museum's Annual Reports which record that Harold St George Gray started work at the Pitt Rivers Museum in Oxford in 1899, replacing J.T. Long.
Bibliography for this article
Bowden, Mark 1991. Pitt Rivers: The Life and Archaeological Work of Lieutenant-General Augustus Henry Lane Fox Pitt Rivers, Cambridge: Cambridge University Press.
Gray, H. St. G. 1905 Excavations in Cranborne Chase vol. V Dorset
Gray, H. St. G. 1905. ‘A Memoir of Lt-General Pitt-Rivers’ in Excavations in Cranborne Chase vol. V. Somerset [privately published] [Available here]
Gray, H. St. G. 1906. Lt General Pitt Rivers in Memoirs of Old Wiltshire Bemrose and Sons London UK
Gray, H. St. G. 1953 [no title] in Anthropology at Oxford: the proceedings of the five-hundredth meeting of the Oxford University Anthropological Society ... February 25th, 1953.
Who Was Who
AP, March 2011