Grothendieck's Theorem, past and present

Probably the most famous of Grothendieck's contributions to Banach space theory is the result that he himself described as ``the fundamental theorem in the metric theory of tensor products''. That is now commonly referred to as ``Grothendieck's theorem'' (``GT'' for short), or sometimes as ``Grothendieck's inequality''. This had a major impact first in Banach space theory (roughly after 1968), then, later on, in C^*