Brown, Robert (1773-1858), a Scottish botanist, is best known for describing the agitation of microscopic particles suspended in a liquid or gas, a movement that is now called Brownian motion.

Robert Brown, the son of an Episcopalian minister, completed his medical studies at the University of Edinburgh and then worked as an assistant surgeon in a Scottish infantry regiment. In the late 1790's, he met well-known botanist Joseph Banks and began to pursue his interest in botany. After resigning his surgical post, Brown served from 1801 to 1805 as the naturalist on an expedition to survey the coast of Australia, which had been recently discovered by Europeans. From 1810 until Banks's death in 1820, Brown served as his librarian. In 1827, Banks's books and collections were transferred to the British Museum, where Brown became curator of the botanical department.

Brown had noted and studied the agitated motion of very fine pollen grains suspended in water. In 1828, his observations of this motion were published. Brown also established that tiny particles of inorganic materials such as carbon and metals display Brownian motion. Brownian motion proved important to the development of the atomic theory of matter, which states that matter is composed of small particles in random motion.

Among his other contributions, Brown gave the name nucleus to the specialized body that regulates the functions of a living cell and was the first to identify it as a feature of most living cells. In addition to naming the world's largest flower—the giant rafflesia of Sumatra, which can grow more than 3 feet (91 centimeters) wide— Brown also began the study of plant fossils, using a microscope.