As soon as trucks that could haul stuff were invented, someone decided it would be good to be able to dump that stuff out the back, and the dump truck was born (I over-simplify, of course...there were dump-horse-drawn-wagons even in the late 1800s). Since everyone loves dump trucks (ok, I did as a little boy, so I'm projecting), here are a couple of very early ones.
Possibly a Ford AA?
A guy with a job that was the envy of many a little boy
Want more? Here's another site with great photos of old trucks.