"First" use of 'Category theory' to describe our field

Hi all, the (idle) question is: when did the phrase 'category theory' catch on for the field? Clearly it didn't leap from either of the heads of Eilenberg or Mac Lane full-grown, since they used the phrase 'General theory of natural equivalences'. There are the old 'Reports of the Midwest Category Seminar' lecture notes (the first in 1967), which hints that 'category theory' wasn't quite the name in use. Even more interesting: who was the first "category theorist", by that name? Answers referring to verifiable sources would be best. Thoughts? David David Roberts Webpage: https://ncatlab.org/nlab/show/David+Roberts Blog: https://thehighergeometer.wordpress.com [For admin and other information see: http://www.mta.ca/~cat-dist/ ]