Hendrik Lorentz - Brief biography.

Aleksandr FriedmannHermann Weyl - One of the first people to combine general relativity with the laws of electromagnetism

Edwin Hubble - Top-biography.com - Site provides Full Biograpraphy, Cosmology, Hubble's Laws, Significant Discoveries, Chronology, Honors and Achievements, Quotations, Chronology & Images of famous astronomer & scientist Edwin Hubble.

Edwin Hubble - Lawyer-turned-astronomer who photographed the galaxies

Karl Schwarzschild - The man who solved Einstein's equations and predicted the existence of black holes

Marcel Grossmann - A brief biography on Marcel Grossmann, a classmate of Einstein who was the first to find a connection between tensor calculus and the theory of relativity.

Georg Riemann - Although he died before the development of general relativity, his work in non-Euclidean geometries is very important to studying a curved spacetime.

Willem DeSitter - Mathematician who studied solution to general relativity and developed DeSitter space

Georgio Ricci-Curbastro - The mathematician who developed much of tensor calculus before Einstein found a use for it.

Luigi Bianchi - A mathematician who developed many theorems regarding Riemannian geometry