Major-General William Roy FRS (4 May 1726 – 1 July 1790) was a Scottish military engineer, surveyor, and antiquarian. He was an innovator who applied new scientific discoveries and newly emerging technologies to the accurate geodetic mapping of Great Britain.It was Roy's advocacy and leadership that led to the creation of the Ordnance Survey in 1791, the year after his death. His technical work in the establishment of a surveying baseline won him the Copley Medal in 1785. His maps and drawings of Roman archaeological sites in Scotland were the first accurate and systematic study of the subject, and have not been improved upon even today. Roy was a Fellow of the Royal Society and a member of the Society of Antiquaries of London.