Sir Francis Galton FRS FRAI (/ˈɡɔːltən/; 16 February 1822 – 17 January 1911) was an English polymath and the originator of eugenics during the Victorian era; his ideas later became the basis of behavioural genetics.

Galton produced over 340 papers and books. He also developed the statistical concept of correlation and widely promoted regression toward the mean. He was the first to apply statistical methods to the study of human differences and inheritance of intelligence, and introduced the use of questionnaires and surveys for collecting data on human communities, which he needed for genealogical and biographical works and for his anthropometric studies. He popularised the phrase "nature versus nurture". His book Hereditary Genius (1869) was the first social scientific attempt to study genius and greatness.

As an investigator of the human mind, he founded psychometrics and differential psychology, as well as the lexical hypothesis of personality. He devised a method for classifying fingerprints that proved useful in forensic science. He also conducted research on the power of prayer, concluding it had none due to its null effects on the longevity of those prayed for. His quest for the scientific principles of diverse phenomena extended even to the optimal method for making tea. As the initiator of scientific meteorology, he devised the first weather map, proposed a theory of anticyclones, and was the first to establish a complete record of short-term climatic phenomena on a European scale. He also invented the Galton whistle for testing differential hearing ability. Galton was knighted in 1909 for his contributions to science. He was Charles Darwin's half-cousin.

In recent years, he has received significant criticism for being a proponent of social Darwinism, eugenics, and biological racism; indeed he was a pioneer of eugenics, coining the term itself in 1883.

Galton is credited with popularizing the phrase "nature versus nurture" to frame the academic discussion regarding the relative influence of heredity and environment on human ability and social advancement.

Galton was born at "The Larches", a large house in the Sparkbrook area of Birmingham, England, built on the site of "Fair Hill", the former home of Joseph Priestley, which the botanist William Withering had renamed. He was Charles Darwin's half-cousin, sharing the common grandparent Erasmus Darwin. His father was Samuel Tertius Galton, son of Samuel Galton Jr. He was also a cousin of Douglas Strutt Galton. The Galtons were Quaker gun-manufacturers and bankers, while the Darwins were involved in medicine and science.

Both the Galton and Darwin families included Fellows of the Royal Society and members who loved to invent in their spare time. Both Erasmus Darwin and Samuel Galton were founding members of the Lunar Society of Birmingham, which included Matthew Boulton, James Watt, Josiah Wedgwood, Joseph Priestley and Richard Lovell Edgeworth. Both families were known for their literary talent. Erasmus Darwin composed lengthy technical treatises in verse. Galton's aunt Mary Anne Galton wrote on aesthetics and religion, and her autobiography detailed the environment of her childhood populated by Lunar Society members.

Galton was a child prodigy – he was reading by the age of two; at age five he knew some Greek, Latin and long division, and by the age of six he had moved on to adult books, including Shakespeare for pleasure, and poetry, which he quoted at length. Galton attended King Edward's School, Birmingham, but chafed at the narrow classical curriculum and left at 16. His parents pressed him to enter the medical profession, and he studied for two years at Birmingham General Hospital and King's College London Medical School. He followed this up with mathematical studies at Trinity College, Cambridge, from 1840 to early 1844.