Legendre was educated at the Collège Mazarin in Paris. In 1775 he taught with Laplace at the École Militaire. Legendre’s career covered many branches of mathematics and, in 1805, he published the first account of the method of least squares.

http://www.maths.tcd.ie/pub/HistMath/People/Legendre/RouseBall/RB_Legendre.html Fuller biography.