In Phineas and Ferb, the joke is that humans think platypuses don't do anything, and yet Perry is actually a secret agent. Even though "Perry doesn't do anything," they love him and he's important to them.
Years earlier, Phil Foglio introduced a The Winslow, a platypus-like indestructible reptile who's important to "everyone," but doesn't do anything.
This is the earliest example of this trope that I have found. Is anyone aware of an earlier example?