Story I heard was that a GM excecutive's wife always wanted a convertable but never put the top down. He asked her why she never put the top down and she said she liked the look of no post with the windows down. So, he went to the design engineers with her comment and the hardtop was born. That's why some hardtops, like the 63 Impala, have lines in the top that simulate convertable roof bows. Urban myth??
49 Cadillac, Buick and Olds had the first production hardtops. http://auto.howstuffworks.com/1949-cadillac-series-sixty-two-coupe-de-ville.htm
Yes, GM made the first production hardtops...Buick, Caddy, and Olds. But the hardtop was a MoPar innovation; Behold, the one-off 1946 Chrysler Town & Country
I've heard the same story. Interestingly, there used to be an elderly lady here who drove a 55 Bel-Air conv. she bought new. Never put down the top, she just loved the look. She died a few years back-haven't seen the car since. P.S. She had signs in each quarter window that read: NOT FOR SALE.
There were several companies in California who built removable hardtops for both roadsters and tourings from the late teens on into the twenties. They were often known as "Californian" tops no matter where they were sold. These were aftermarket tops which were removable for good weather, not true factory hardtops. The Budd Company, of Philadelphia, was an early innovator in the stamping of sheet metal for the auto industry. As early as 1916 they built a production four door hardtop body for Dodge Bros.
That is the most realistic reason I have ever heard. Most great inventions come from the most unlikey source.
I've heard this story as Harley Earl's wife always got a Buick convertable and never put the top down.
"Edward T. Ragsdale, Buick manufacturing manager and later general manager, helped inspire the hardtop convertible styling. Ragsdale noticed that his wife Sarah always ordered convertibles, but never put the top down. She said she liked the styling but didn't want to muss her hair." http://www.buickheritagealliance.org/buickhistory.php
The early Model T Ford Coupe @1918 had a removable B pillar so you could say it was a hardtop once the post was removed.