Henry John Stephen Smith, mathematician and amateur astronomer, is born in Dublin on November 2, 1826. He is remembered for his work in elementary divisors, quadratic forms, and Smith–Minkowski–Siegel mass formula in number theory. In matrix theory he is visible today in having his name on the Smith normal form of a matrix. He is also first to discover the Cantor set.

Smith is the fourth child of John Smith (1792–1828), a barrister, who dies when Henry is two. His mother, Mary Murphy (d.1857) from Bantry Bay, very soon afterward moves the family to England. He has thirteen siblings, including Eleanor Smith, who becomes a prominent educational activist. He lives in several places in England as a boy. His mother does not send him to school but educates him herself until age 11, at which point she hires private tutors. In 1841, at the age of 15, he is admitted to Rugby School in Warwickshire, where Thomas Arnold is the school’s headmaster. This comes about because his tutor, Henry Highton, takes up a housemaster position there.

At the age of 19 Smith wins an entrance scholarship to Balliol College, Oxford. He graduates in 1849 with high honours in both mathematics and classics. He is fluent in French having spent holidays in France, and he takes classes in mathematics at the College of Sorbonne in Paris during the 1846–47 academic year. He is unmarried and lives with his mother until her death in 1857. He then brings his sister, Eleanor, to live with him as housekeeper at St. Giles.

Smith remains at Balliol College as a mathematics tutor following his graduation in 1849 and is soon promoted to Fellow status.

In 1861, Smith is promoted to the Savilian Chair of Geometry at the University of Oxford. In 1873, he is made the beneficiary of a fellowship at Corpus Christi College, Oxford, and gives up teaching at Balliol College.

In 1874, Smith becomes Keeper of the University Museum and moves, along with his sister, to the Keeper’s House on South Parks Road in Oxford.

On account of his ability as a man of affairs, Smith is in demand for academic administrative and committee work: he is Keeper of the Oxford University Museum of Natural History, a Mathematical Examiner for the University of London, a member of a Royal Commission to review scientific education practice, a member of the commission to reform University of Oxford governance, chairman of the committee of scientists overseeing the Meteorological Office and twice president of the London Mathematical Society.

Smith dies in Oxford on February 9, 1883. He is buried in St. Sepulchre’s Cemetery in Oxford.