Though I played with mathematics, I was an architect and military engineer in Lyons.
In 1639, I wrote Rough Draft of an Attempt to Deal with the Outcome of a Meeting of a Cone and a Plane, considered to be one of the most unsuccessful books every published...only one hand-written copy exists today in a Paris library.
In the area of projective geometry, I introduced many new terms that no one liked, such as calling a conic section a "coup de rouleau" (that is, incidence with a rolling pin).
I was a friend of Rene Descartes, and was with him in 1628 at the seige of LaRochelle.
A famous theorem is named after me, and even served as a painting on a wall in a mathematics classroom: If two triangles are so situated that lines joining pairs of corresponding vertices are concurrent, then the points of intersection of pairs of corresponding sides are co-linear, and conversely.
Girard Desargues (1591-1661)