Casper the Friendly Ghost in "There's Good Boos Tonight", 1948. Probably the darkest and most depressing of these usually too-cute cartoons.
Which reminds me of a Simpson's quote:
Bart: I think Casper's the ghost of Richie Rich.
Lisa: Hey! They do look alike.
Bart: I wonder how Richie died?
Lisa: Perhaps he realized how hollow the pursuit of money is and took his own life.