"She's so fine, my 409"
No, the car wasn't called a 409, but people referred to them as 409's anyway, like people used to refer to Mustangs at 5.0's.
They were the grandfather of the modern day big block Chevy engines, which, as Compuwiz mentioned, started with the 396.
You really could say they were also somewhat responsible for the Ford 429 and 460 big blocks, and the 351 Clevelands, too, since Ford admittedly copied the canted valve design from Chevrolet.