I just followed a chain of links starting with Teri Cettina‘s article in The Costco Connection magazine about a puzzle folk-artist named Eric Dowdle. There was a reference to a time when puzzles were given out as free premiums with toothpaste around the time of Great Depression. I had to pursue this.
Turns out, I discovered a book (which I will have to read) called The Puzzle King, written in 2009 by Betsy Carter. In this historical fiction based on myths, memories and research, Carter bases one of the main characters on her great-uncle Morris Einson, a turn-of-the-century Lithuanian immigrant who became a wealthy Yonkers advertising executive.
In the book, Einson (as Simon Phelps) invents Monopoly. In truth, he did not; what he did figure out was how to make jigsaw puzzles out of inexpensive cardboard instead of expensive wood. Einson was a pioneer in window and store display advertising, and at one point, evidently, he had to the idea to give out a puzzle with a purchase of Pepsodent toothpaste.
Puzzles. Pepsodent. I love connections.