Albert Einstein byl ten muž, který napsal teorii relativity. Albert Einstein byl ten muž, kdo napsal teorii relativity. * Is there any difference? Are they always interchangeable or is there some defining vs. non defining rule like in English? Sorry if someone has asked this before! *some other poor sod wrote the theory of relativity and gets no credit for it among the general public, Einstein wrote: Relativity: The Special and General Theory but who among us could tell the difference?