Physician, scientist, writer.

Practiced medicine in South America without formal schooling. Moved to England (c. 1767), where he met Franklin and Joseph Priestley, who helped secure his election to The Royal Society (1773).

Initially seemed to support the American cause and worked as a spy for Franklin in London (1776). Became secretary to the American Commissioners in France (1776), acting as a spy for the British. Franklin and Deane never suspected Bancroft; indeed, his role as a British agent was not discovered until long after his death. Maintained a friendly correspondence with Franklin after the war.

Well-known in later years as a chemist for his work with dyes.

Born in Westfield, Massachusetts. Father of Edward Nathaniel Bancroft.