Lambert Adolphe Jacques Quetelet FRSF or FRSE (French: [kətlɛ] ⓘ; 22 February 1796 – 17 February 1874)[1] was a Belgian astronomer, mathematician, statistician and sociologist who founded and directed the Brussels Observatory and was influential in introducing statistical methods to the social sciences.

[4] His work on measuring human characteristic to determine the ideal l'homme moyen ("the average man"), played a key role in the origins of eugenics.

His father was born at Ham, Picardy, and being of a somewhat adventurous spirit, he crossed the English Channel and became both a British citizen and the secretary of a Scottish nobleman.

Shortly thereafter, the young man set out to convince government officials and private donors to build an astronomical observatory in Brussels; he succeeded in 1828.

[8] From 1841 to 1851, he was a supernumerary associate in the institute, and when it became Royal Netherlands Academy of Arts and Sciences he became foreign member.

He made significant contributions to scientific development, but he also wrote several monographs directed to the general public.

His most influential book was Sur l'homme et le développement de ses facultés, ou Essai de physique sociale, published in 1835 (In English translation, it is titled Treatise on Man, but a literal translation would be "On Man and the Development of his Faculties, or Essay on Social Physics").

In it, he outlines the project of a social physics and describes his concept of the "average man" (l'homme moyen) who is characterized by the mean values of measured variables that follow a normal distribution.

He saw the average body as an ideal beauty and something to be desired and his work was influential on Francis Galton who coined the term eugenics.

Nightingale met Quetelet in person at the 1860 International Statistical Congress in London, and they corresponded for years afterwards.

Other influential factors he found included climate, poverty, education, and alcohol consumption, with his research findings published in Of the Development of the Propensity to Crime.

[14] In terms of influence over later public health agendas, one of Quetelet's lasting legacies was the establishment of a simple measure for classifying people's weight relative to an ideal for their height.