Arnie Cunningham's the kid we're supposed to root for, but honestly, I spent half the book thinking the Plymouth itself was the main character. The way King writes 'Christine', the car's consciousness bleeds into everything. It feels less like a guy and his possessed car, and more like a toxic relationship where the car's the dominant personality. Arnie changes so drastically from a bullied, awkward teenager to this arrogant, possessive guy that the person at the start barely resembles the one at the end. You could argue the real protagonist is the corruption, with Arnie and 'Christine' just being the vessels.
Leigh Cabot, his girlfriend, gets sidelined pretty hard in the narrative, which is a shame because her perspective on Arnie's transformation is the most grounded. The story's really told through Dennis Guilder, Arnie's best friend, so sometimes it feels like Dennis is the lens, even if Arnie is the subject. The whole thing is messy in a classic King way—you're never quite sure who to pin the protagonist label on, which might be the point when dealing with a force of evil like that car.