The society has numbered many prominent scientists amongst its fellows. One such was the botanist Robert Brown, who was librarian, and later president (1849–1853); he named the cell nucleus and discovered Brownian motion.[5] In 1854 Charles Darwin was elected a fellow; he is undoubtedly the most illustrious scientist ever to appear on the membership rolls of the society.[2]: 53 Another famous fellow was biologist Thomas Huxley, who would later gain the nickname "Darwin's bulldog" for his outspoken defence of Darwin and evolution.