Apollonius of Perga (c. 262-190 B.C.)  
   known as 'The Great Geometer', great influence on the development of mathematics, famous book Conics introduced terms such as parabola, ellipse and hyperbola.
   http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Apollonius.html

Pappus of Alexandria (c. 320)  
   Wrote treatise, the Mathematical Collection, as a guide to Greek geometry, discusses theorems and constructions of more than thirty different mathematicians of antiquity.
   http://www.lib.virginia.edu/science/parshall/pappus.html

Steiner, Jakob (1796-1863)  
   Was one of the greatest contributors to projective geometry.
   http://turnbull.dcs.st-and.ac.uk/history/Mathematicians/Steiner.html

Riemann, Georg Friedrich Bernhard (1826-1866)  
   Theory of functions, non-Euclidian geometry, relativity theory, Famous for the Riemann hypothesis about the behavior of zeros of the Riemann zeta function, which he showed determines the distribution of prime numbers.
   http://turnbull.dcs.st-and.ac.uk/history/Mathematicians/Riemann.html

Desargues - Girard Desargues (1591-1661)  
   Founder of projective geometry, his work centred on the theory of conic sections and perspective.
   http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Desargues.html

Heron of Alexandria (ca. 75 AD)  
   Greek mathematician who was mainly interested in practical studies in mechanics and engineering, best known for Heron's Formula
   http://scienceworld.wolfram.com/biography/Heron.html

Klein, Felix (1849-1925)  
   Plücker's assistant at Bonn who studied Analytic Geometry, describing geometry as the study of properties of figures which remain invariant under a Group of Transformations. He systemized Non-Euclidean Geometry.
   http://scienceworld.wolfram.com/biography/KleinFelix.html

Monge, Gaspard - Conte de Péluse (1746-1818)  
   The father of differential geometry, he devised a system called Geometrie descriptive, now known as orthographic projection, the graphical method used in modern mechanical drawing.
   http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Monge.html