Gauss and Weber taught Riemann, one of the most important mathematicians of the 19thC, Gauss encouraging his famous work on the foundations of geometry. He also studied with Dirichlet and Eisenstein (both influential), and with Steiner and Jacobi. As Weber’s assistant, he helped with his and Kohlrausch’s research. Listing influenced his ideas about topology. Dedekind, a friend from student days, went to the Harz with him, and edited his work for publication after his early death. He met Kummer and Weierstrass in Berlin, Hermite and Bertrand in Paris, and stayed with Betti in Italy. Borchardt was his greatest correspondent.