“Jeep” and “goon” were both coined by Elzie Segar for his comic strip, Thimble Theatre, starring Popeye.
“Milquetoast” was introduced in cartoonist Harold Webster’s strip, The Timid Soul. His lead character, Caspar Milquetoast, was named after “milk toast,” a bland dish served to people with digestion problems, and the word soon became a slang term for someone who is meek or weak.
I heard that it derived from the word robotniki, which means peasant.
At any rate, there is agreement that it was a new formation when used in the title of his play.
Much like the word robotics, which is credited as a creation of Issiac Asimov, although he modestly demurred that it was merely the logical grammatical construction. Sort of how the study of something is generally given a name like (something)ology: do we really need to give credit to the first person to parse that construction?
In that case at least, I say yes: if it took several decades and still nobody had done it, then maybe the idea wasn’t as obvious as it seems. Apparently nobody before Asimov had thought robots might be a field of study worthy of a name.
Sorry. My post contained a typo (Issac Asimov) and an omitted word ("Sort of like how the study of something …).
And my browser crashed right after posting, so I missed the edit window. 
It should.
Shipoopi, invented by Meredith Willson.
What’s that you say? Never used outside the song? And you’ve never heard of Meredith Willson either? Harumph!