We love Tolkien, but he's not always what you would call subtle. He likes to come right out there and say what people are like. Take, for example, his representation of the Mouth of Sauron: "At [the embassy's] head rode a tall and evil shape, mounted upon a black horse, if horse it was; for it was huge and hideous" (5.10.30). We know this messenger is bad not only because he works for Sauron, but also because Tolkien comes out and tells us as much. Even his shape is "tall and evil." You can't get much more direct than that.
We've said in our other learning guides that good characters in Tolkien tend to look good, while bad characters tend to look, um, bad. That holds true in The Return of the King as well. Even with figures who are a bit more morally ambiguous than Shagrat (bad) or Galadriel (good), appearance still tells us a lot. Just take, for example, everyone's least favorite Steward. Denethor starts out as a good man but has the potential to go wrong. We get indications of this in his first introduction to Pippin:
Denethor looked indeed much more like a great wizard than Gandalf did, more kingly, beautiful, and powerful; and older. Yet by a sense other than sight Pippin perceived that Gandalf had the greater power and the deeper wisdom, and a majesty that was veiled. (5.1.78)
Denethor's ancient, proud face impresses Pippin with its sternness and wisdom (which makes sense, since he is a man of great authority and power). At the same time, Pippin notices something off about him, something that makes him less than Gandalf. Denethor looks the part of the majestic old wizard, but we know that Gandalf is the greater of the two.
The orcs' coarse talk in the tower at Cirith Ungol indicates that they are a bunch of violent jerks. Sam overhears Shagrat shouting to one of his orc traitors, "So that's it, is it? […] I'll put red maggot-holes in your belly first" (6.1.51). "Maggot-holes" in his "belly"? That's very different language from Éomer's formal question at the Houses of Healing about Faramir: "Has any hurt befallen him?" (5.8.39). The high, almost poetic speech of the Riders of Rohan and the men of Gondor indicate their honorable and virtuous natures. The violence of the orcs' words—and their frequent sneers and jibes—proves just how demonic they are. Each character's mode of speaking says a lot about his or her overall moral character in this series. (See our "Character Analysis" of Ghân-buri-Ghân for another interesting example of speech as a characterization tool in The Return of the King.)
We keep saying that "type of being" obviously matters a lot to Tolkien's characterization: if you're an Ent, you like forests; if you're a hobbit, you like smoking; if you're an orc, you're, well, gross. But those boundaries, which seemed so important in the earlier novels, start to break down in The Return of the King.
In this final volume, Tolkien focuses much more on men and their flaws than on the differences between elves, dwarves, hobbits, and men in general. We see Southrons and Wild Men and men of Gondor and men of Rohan, all with different wishes and points of view. This emphasis on men points to Middle-earth's post-Sauron future, in which there will be fewer elves and dwarves left to contrast to humans. So humans must contrast themselves.
By the end of The Return of the King, Aragorn's decision to marry an elf (Arwen) and Arwen's choice to bring a hobbit-maid (Elanor, Rosie and Sam's daughter) to her court (see Appendix A, iii, 22) both show that the barriers between the different races of Middle-earth are becoming less rigid.
Yet, even if "type of being" is a less important mode of characterization in The Return of the King, it still matters: the Appendices give the histories of Middle-earth's peoples separately, reinforcing that dwarfish life and elvish life remain pretty different.