1948, the Manchester Baby.
Yes it was only a proof of concept prototype computer with only 32 words of 32 bit CRT DRAM, but it worked and proved the basic concepts used in all modern computers. Everything since have only been refinements.
They did not build a computer they built a server.
1785
In USA
J.H. Müller
Depends on what you mean by "modern".
50cm
What did the first Spanish settlers in the West build there?
1906
The first computer was invented in 1946
no one
no. but he did invent the first general purpose programmable computer invented.
the military