Godfrey Harold Hardy (1877-1947) was educated at Cranleigh, Winchester, and Trinity College, Cambridge, of which he became a fellow in 1900. He became Cayley lecturer in mathematics at Cambridge in 1914, and Savilian professor of geometry at Oxford, 1920. From 1931 to 1932 he was Sadleirian professor of pure mathematics at Cambridge. Hardy produced much of his work in collaboration with other mathematicians, notably J.E. Littlewood. His works include A course of pure mathematics (1908), An introduction to the theory of numbers (1938, with E.M. Wright), and Divergent series (1949). He also contributed to the field of genetics by a developing a law that described how the proportions of dominant and recessive genetic traits would be propagated in a large population.
Srinivasa Aiyangar Ramanujan (1887-1920) was born in in Erode, Tamil Nadu state, India. He taught himself pure mathematics from a textbook by G.S. Carr, and developed his reputation in Madras. After writing to mathematicians in England, he was invited to Cambridge by G.H. Hardy, and became a Fellow of Trinity College (1918-1920). He worked with Hardy between 1914-1920, and after his death Hardy edited his collected works and published Ramanujan: twelve lectures on subjects suggested by his life and work (1940). Ramanujan made original contributions to function theory, power series, and number theory, before he died of tuberculosis.
John Edensor Littlewood (1885-1977) was educated at St. Paul's School, London, before entering Trinity College, Cambridge, in 1903. He was Richardson lecturer at Manchester from 1907 to 1910. In 1908 he became a fellow of Trinity, and in 1910 he was appointed college lecturer. Soon after he began his long collaboration with G.H. Hardy, with whom he wrote many papers. Littlewood was Cayley lecturer at Cambridge, 1920-1928, before occupying the Rouse Ball chair of mathematics, 1928-1950. His works include The theory of real functions (1926) and Lectures on the theory of functions (1944).
From the guide to the Godfrey Harold Hardy: Mathematical Papers, c. 1916-1921, (Cambridge University Library, Department of Manuscripts and University Archives)