He doesn't get much screen time, but the wolf that Brian meets in Chapter 13 is a pretty big deal when it comes to symbolism. Let's take a look.
While hunting on the edge of the lake, Brian senses something, something that makes him stop what he's doing and hold perfectly still. Turning his head slightly, he sees a wolf watching him. The wolf is "not as big as a bear but somehow seeming that large" (13.7)—definitely a dangerous, powerful animal.
While Brian does feel a fleeting sense of fear, the final impression created is one of peacefulness and belonging. Hmmm. Has he never read Grimm's fairy tales? But really, there's an understanding between Brian and the wolf, as between two parts of a bigger whole:
The wolf claimed all that was below him as his own, took Brian as his own. […]
[Brian] knew the wolf for what it was—another part of the woods, another part of all of it. (13.7-8)
Brian's acceptance of the wolf—both its power and its beauty—can be read as a symbol of his new relationship with nature and his new sense of his own place in the natural world. When he discovers the wolf watching him, he reacts not with fear but with calm understanding. Compare this to Brian's frightened, panicked reaction when he first stumbles across the bear in the berry patch, and you can see just how much Brian—and his relationship with nature—has changed during his time in the woods.