Sir Thomas Gresham (c. 1519 – 21 November 1579), Thomas Gresham the Elder, was an English merchant and financier who acted on behalf of King Edward VI (1547-1553) and Edward's half-sisters, queens Mary I (1553-1558) and Elizabeth I (1558-1603).
In 1565 Gresham founded the Royal Exchange in the City of London.
Born in London and descended from an old Norfolk family, Gresham was one of two sons and two daughters of Sir Richard Gresham, a leading City merchant mercer and Lord Mayor of London, who was knighted by King Henry VIII for negotiating favourable loans with foreign merchants.
Although his father wanted Thomas to become a merchant, Sir Richard first sent him to receive a university education at Gonville and Caius College, Cambridge, and was concurrently apprenticed in the Mercers' Company to his uncle Sir John Gresham (founder of Gresham's School (1555)), whilst up at Cambridge.
In 1543 the Mercers' Company admitted the 24-year-old Gresham as a liveryman, and later that year he left England for the Low Countries, where, either on his own account or that of his father or uncle, he both carried on business as a merchant whilst acting in various matters as agent for King Henry VIII. In 1544 he married Anne Ferneley, widow of the London merchant Sir William Read, but maintained residence principally in the Low Countries, basing his headquarters at Antwerp in present-day Belgium (then the Spanish Netherlands), where he became renowned for his adept market-play.