1) Bernhard riemann 2) German mathematician Bernhard 3) German surname 4) Mathematician 
[crater] This is a heavily battered and eroded formation that is only a remnant of its former self. The outer rim has been worn away in many places, and now forms an irregular series of ridges in a rough circle. The rim is overlain along the south-southwestern rim by Beals, and several smaller craters lie along the western and southeast rim...
[n] - pioneer of non-Euclidean geometry (1826-1866)
Bernhard Riemann noun pioneer of non-Euclidean geometry (1826-1866)