Merchant and philanthropist. Known as 'Floating Bob', Preston made a vast personal fortune through trade in the East Indies. He owned houses in Essex and a home in Downing Street (London), but in 1800 inherited the Baronetcy of Valleyfield in West Fife. He set about improving this estate and commissioned the English landscape architect Sir Humphrey Repton (1752 - 1818) to create a romantic parkland around Valleyfield House. He also developed local salt works and coal mines.
Preston was well connected socially, both in London and Edinburgh. His circle of friends included politician William Pitt the Younger (1759 - 1806), author Sir Walter Scott (1771 - 1832), traveller James Boswell (1740-95), and the painters Alexander Nasmyth (1758 - 1840) and J.M.W. Turner (1775 - 1851). He was also known for his appetite, with Scott commenting that he "was as big as two men, and eats like three", yet was known to donate excess food to the poor. He also create The Valleyfield Endowment to provide financial help to the poor of Culross and Torryburn.