The Original Superman Animated Cartoon
Before Fleischer Studios had even started working on their now-famous Superman cartoons, the Man of Steel made his first animated appearance in Goofy Groceries, a Warner Brothers cartoon directed by Bob Clampett. He's depiected as the mascot for Superguy Soap Chips, and races into action to stop a giant gorilla. The gorilla scares him into baby-hood -- well over a decade before Superbaby is introduced in DC comics. Also worth mentioning that we're still looking at 191 here, so the stylized S-shield in this cartoon is pretty accurate to the comics of the time!
(h/t Brendan Spillane)