In between the absolute good of Scott and the absolute evil of Beauty sits Grey Beaver: convenient racial stereotype who inducts White Fang into the messed up world of men. We see Grey Beaver almost entirely from White Fang's perspective—The Man-God! The Bringer of Fire!—and the rest remains largely in the realm of stereotyping.
Grey Beaver uses White Fang as a tool, rewarding good behavior and punishing bad behavior, but never showing any human emotions like love or respect. He's loyal to White Fang in the way that a boss is loyal to an underling, because the underling does his bidding: "They went away with vengeance unsatisfied. Grey Beaver defended White Fang" (13.20). That loyalty doesn't come from affection or connection, but rather a sense that White Fang represents him, is useful to him, and would probably be a good creature to keep around. And that loyalty pretty much flies right out the window when Grey Beaver trades White Fang for a bottle of whiskey. So we know where his priorities lie.
That last part raises the difficult question of stereotyping. London clearly doesn't think much of Grey Beaver, which reflects a larger contempt for Native American culture at the time. Phrases like "Grey Beaver was as a child-god among these white-skinned ones" (15.17) certainly don't help matters. London depicts Grey Beaver's status as a Native American as making him inferior to "a race of superior gods" (15.17). If that doesn't make you cringe, we don't know what will. He seems to suggest that Grey Beaver's not as civilized (whatever that means) as his white counterparts in the Yukon, because they have "greater mastery over matter" (15.17).
On the other hand, he also shows white men as being far worse in many ways. If London actually wants us to think that Beauty Smith is superior to Grey Beaver in any way, we'll eat our hat. Grey Beaver might not be any great shakes as a man, but he understands the natural world, which London can't jump on too hard. He's a stepping-stone between the wild world and the civilized one: leading White Fang to both his most agonizing torments and his eventual happy ending.
Then again, depicting Native Americans as some how more in tune with Nature-with-a-capital-N is a stereotype in and of itself, so we can't let London off the hook quite yet. We're gonna leave it up to you, Shmoopers, to make the call: is Grey Beaver more than a London-drawn stereotype of Native Americans?