Okay, yeah, we know—Charley is a dog, so what's he doing in the "Characters" section? We get your point. However, as you may have noticed from reading the book, Steinbeck sees all kinds of human qualities in Charley and even imagines him as participating in full dialogues about his feelings and intentions. Plus, he actually gets the most robust characterization of anyone in the book. So, without further ado, here's what you need to know about the French poodle.
He's not even just regal—Steinbeck describes him as a "gentleman poodle" with a fancier background and finer sensibilities and problems than most humans. This is how Steinbeck introduces him:
Actually his name is Charles le Chien. He was born in Bercy on the outskirts of Paris and trained in France, and while he knows a little poodle English, he responds quickly only to commands in French. Otherwise he has to translate, and that slows him down. He is a very big poodle, of a color called bleu, and he is blue when he is clean. Charley is a born diplomat. He prefers negotiation to fighting, and properly so, since he is very bad at fighting. Only once in his ten years has he been in trouble—when he met a dog who refused to negotiate. (1.2.14)
So, yeah, that gives you a pretty good idea of the kind of character (and, in Steinbeck's case, psychosis) we're dealing with. Charley is sophisticated enough to prefer negotiating to street fighting, and he's a "diplomat"—say what? Also, unlike most Americans, the dog is bilingual. So yeah, he's got a more impressive resume and a stronger interest in diplomacy than most folks and he's not even... folks.
Oh, and we should also probably mention that he's named for Steinbeck's uncle.
Charley's actually got a fair amount of pride and a strong sense of dignity, and he can get kind of haughty when he feels he's been wronged. All of these qualities are in full display when Steinbeck picks Charley up from being groomed and boarded while Steinbeck was in Chicago:
Charley was torn three ways—with anger at me for leaving him, with gladness at the sight of Rocinante, and with pure pride in his appearance. For when Charley is groomed and clipped and washed he is as pleased with himself as is a man with a good tailor or a woman newly patinaed by a beauty parlor, all of whom can believe they are like that clear through. Charley's combed columns of legs were noble things, his cap of silver blue fur was rakish, and he carried the pompon of his tail like the baton of a bandmaster. A wealth of combed and clipped mustache gave him the appearance and attitude of a French rake of the nineteenth century, and incidentally concealed his crooked front teeth. I happen to now what he looks like without the tailoring. One summer when his fur grew matted and mildewed I clipped him to the skin. Under those sturdy towers of legs are spindly shanks, thin and not too straight; with his chest ruff removed one can see the sagging stomach of the middle-aged. But if Charley was aware of his deep-down inadequacy, he gave no sign. If manners maketh man, then manner and grooming maketh poodle. He sat straight and nobly in the seat of Rocinante and he gave me to understand that while forgiveness was not impossible, I would have to work for it. (3.1.4)
First of all, Charley is not pleased that Steinbeck left him, and he lets his displeasure be known. Also, we learn that Charley feels particularly proud and dignified after his bath, but he naturally feels pretty sure of himself most of the time, even when he's not as immaculately groomed.
Yup, in addition to looking good and knowing it, Charley only associates with the smartest, most intelligent people, according to Steinbeck. He's also extremely intuitive:
He has always associated with the learned, the gentle, the literate, and the reasonable both in France and in America. And Charley is no more like a dog dog than he is like a cat. His perceptions are sharp and delicate and he is a mind-reader. I don't know that he can read the thoughts of other dogs, but he can read mine. Before a plan is half formed in my mind, Charley knows about it, and he knows whether he is to be included in it. There's no question about this. (3.3.14)
Steinbeck claims a couple of different times that he thinks Charley can read minds, and whether he literally believes that to be true, he's certainly suggesting that, at the very least, Charley is attuned to what's going on around him and can reason pretty well. In Steinbeck's view, this means he's really more like a human than a dog.
Despite all of Steinbeck's claims that his dog isn't like other dogs, Charley does have one very dog-like trait: strong, irrational, no-good feelings toward other animals (sometimes). All Charley's diplomacy and reasonableness go out the window when he sees bears, for example:
To the best of my knowledge Charley had never seen a bear, and in his whole history had showed great tolerance for every living thing. Besides all this, Charley is a coward, so deep-seated a coward that he has developed a technique for concealing it. And yet he showed every evidence of wanting to get out and murder a bear that outweighed him a thousand to one. I don't understand it. (3.6.10)
Charley gets all aggressive with the bears even though this makes zero sense—the bears could clearly take him—and basically works against Steinbeck's image of him as this peace-loving, rational dog who is more reasonable than most humans.