I would like to know who coined the term planar graph?
I was able to trace the term back to a paper "Non-Separable and Planar Graphs" by Hassler Whitney, Proc. Natl. Acad. Sci USA. 1931 February; 17(2): 125–127. Is this the first occurrence?
Obviously, planar graphs have been studied as 1-skeletons of polyhedral genus-0 surfaces before (Euler-Poincare formula), but not under this name.
Addition: Thanks to the pointer of Hagen v. Eitzen I found that in the Bulletin of the AMS 1930, pg 214 the following abstract was listed.
Professors Orrin Frink and P.A.Smith:
Irreducible non-planar graphs. One of the results of this paper is a simple necessary and sufficient condition that an arbitrary linear graph be mappable on a plane. (Received February 10,1930.)
The paper was sent out for publication in Trans. of the ACM, but since Kuratowski's result came out just a few months earlier (and it had a similar proof) it got rejected. So this is the first appearance of the term "non-planar graph" I could found.
By the way, Kuratowski's article was in French, and from my understanding there is no direct analogue for "planar graphs" in the text.