Sir William Pulteney, 5th Baronet (October 1729 – 30 May 1805), known as William Johnstone until 1767, was a Scottish advocate, landowner and politician who sat in the House of Commons between 1768 and 1805. He was reputedly the wealthiest man in Great Britain. He profited from slave plantations in North America, and invested in building developments in Great Britain, including the Pulteney Bridge and other buildings in Bath, buildings on the sea-front at Weymouth in Dorset, and roads in his native Scotland.