Who is the first person to invent a desktop computer?

It is hard to say for sure, but several of the smaller minicomputers of the 1960s (e.g. DEC PDP-8) could and usually did sit on a desktop. However the term "desktop computer" was not created until the microcomputers of the 1980s and did not come into common usage until laptop microcomputers computers became widely available in the 1990s.