Kiowa is pretty much the most decent character in the entire book. He's thoughtful, respects the Vietnamese, isn't a coward, and he even has a sense of humor. We quickly learn that he's Tim's best friend in the war, not that either of them would say the words "best friend." They're way too cool for that.
Kiowa is Native American – he carries his grandfather's hunting hatchet – and was raised Christian. His father teaches Sunday school, and he likes the way it feels inside churches. When he gets reflective about Ted Lavender's death, we know that he's also a good guy. And when Tim needs a friend, Kiowa's there.
But Kiowa's also an important symbol. We mean, come on: he's an American Indian (so, an original American), he's morally the most awesome character in the book, and he drowns in a field of sewage. We'll be talking more explicitly about what this might mean over in the "Symbolism, Imagery, Allegory" section, but we're pretty sure that you can draw your own conclusions.