TITLE: Reference request: Who first proved that right adjoints preserve limits?
QUESTION [7 upvotes]: One of the most famous and unifying theorems in category theory is that right adjoints preserve limits. I wonder: Who was the first one to prove this fact?
The notion of adjoint functors is, of course, due to Daniel Kan. But I couldn't find the mentioned fact in his paper Adjoint Functors.

REPLY [19 votes]: Daniel M. Kan defined adjoint functors in his paper Adjoint functors (written in 1956).
In Chapter II he defines limits and colimits of arbitrary small diagrams
and proves that the limit and colimit functors
are right and left adjoints to the diagonal functor
in Theorems 7.8 and 8.6.
In Chapter III, he defines the notion of a limit-preserving functor
in Definition 13.1.
In Theorem 13.8 and 13.8* he proves that left/right adjoints preserve (co)limits.