There's no record of someone named "Ruska" building the first electron microscope. The credit for this invention goes to Ernst Ruska and Max Knoll, who built the first functional electron microscope in 1931 at the Technical University of Berlin, Germany.

It's important to note that Ernst Ruska is the one who is widely recognized for his contribution to the invention, and he was awarded the Nobel Prize in Physics in 1986 for his work on electron optics and for designing the first electron microscope.