Peter Isaac Thellusson, 1st Baron Rendlesham (13 October 1761 – 16 September 1808), was a British merchant, banker and politician. Thelluson was the eldest son of Peter Thellusson, a wealthy London merchant who had emigrated to Britain from France in 1760, and his wife Ann, daughter of Matthew Woodford. After Thellusson senior's death his considerable estate was embroiled in the Thellusson will case. Peter Isaac was educated at Harrow School and took over the thriving family business from his father. Like his father he also became a director of the Bank of England (1787–1806).