Pierre-Simon Laplace

Introduction
Laplace attended a Benedictine priory school in Beaumont between the ages of 7 and 16. At the age of 16 he entered Caen University intending to study theology. Laplace wrote his first mathematics paper while at Caen. 

At the age of 19, mainly through the influence of d'Alembert, Laplace was appointed to a chair of mathematics at the école Militaire in Paris on the recommendation of d'Alembert. In 1773 he became a member of the Paris Academy of Sciences. In 1785, as examiner at the Royal Artillery Corps, he examined and passed the 16 year old Napoleon Bonaparte. 

During the French Revolution he helped to establish the metric system. He taught calculus at the école Normale and became a member of the French Institute in 1795. Under Napoleon he was a member, then chancellor, of the Senate, received the Legion of Honour in 1805. However Napoleon, in his memoires written on St Hélène, says he removed Laplace from office after only six weeks 

because he brought the spirit of the infinitely small into the government 

Laplace became Count of the Empire in 1806 and he was named a marquis in 1817 after the restoration of the Bourbons. In his later years he lived in Arcueil, where he helped to found the Societe d'Arcueil and encouraged the research of young scientists. 

Laplace presented his famous nebular hypothesis in Exposition du systeme du monde (1796), which viewed the solar system as originating from the contracting and cooling of a large, flattened, and slowly rotating cloud of incandescent gas. 

Laplace discovered the invariability of planetary mean motions. In 1786 he proved that the eccentricities and inclinations of planetary orbits to each other always remain small, constant, and self-correcting. These results appear in his greatest work, Traité du Mécanique Céleste published in 5 volumes over 26 years (1799-1825). 

Laplace also worked on probability and in particular derived the least squares rule. His Théorie Analytique des Probabilités was published in 1812. 

He also worked on differential equations and geodesy. In analysis Laplace introduced the potential function and Laplace coefficients. He also put the theory of mathematical probability on a sound footing. With Antoine Lavoisier he conducted experiments on capillary action and specific heat. He also contributed to the foundations of the mathematical science of electricity and magnetism. 

References

Dictionary of Scientific Biography 
Biography in Encyclopaedia Britannica 
E T Whittaker, Works of Laplace, Mathematical Gazette 33 (1949), 1-12. 
E T Bell, Men of Mathematics (1961). 
M P Corsland, The Society of Arcueil: A View of French Science at the Time of Napoleon I (1967). 
J Fourier, éloge historique de M le Marquis de Laplace, MASIF 10 (1831). 
S M Stigler, The History of Statistics. The Measurement of Uncertainty before 1900 (Cambridge, Mass.-London, 1986), 100- . 
H Bernhard, Laplace, in H Wussing and W Arnold, Biographien bedeutender Mathematiker (Berlin, 1983).