Plato is less a sidekick and more a little abused puppy who starts following Jim around after he's been kicked a few too many times. He's a bit younger than Jim, smaller than him, and significantly more emotionally fragile, and after they become friends, Plato begins to look up to him as a surrogate father figure. It's well-established throughout the film that Plato has been neglected by his parents, raised only by a nanny, and is harboring some thinly-veiled homosexual tendencies (the production codes of the time prevent the filmmakers from coming right out and saying it, but it's pretty obvious), so it's hardly a surprise that he worships the ground Jim walks on. But no matter how confident and together Jim looks, he feels like just as much of a misfit as Plato, so they're a well-matched pair. Some of the greatest moments in the film come when they break into the mansion and Plato, Jim, and Judy create the image of the perfect family unit they've all been desperately wishing for.