The 1938 Y-Job is, without question, one of the most important cars you've never heard of. It's considered by many to be the first true concept car (others were experimental rather than conceptual). The legendary Harley Earl (he also did the first Corvette and is responsible for introducing those wild fins on cars of the '50s) built this car to gauge the public's interest in the styling.
Every Buick that followed until the end of the 1950s (see: the 1949 Roadmaster in Rain Man) had the Y-Job to thank for its styling, and its grill is still found on Buicks today.
Aaron Miller is the Rides editor for Supercompressor, and can be found on Twitter. He's seen plenty of concept cars in person, but never any of these.