Jill Pole
Jill is the viewpoint character for most of the book. She receives the signs from Aslan and is responsible for remembering them. She fails repeatedly, partly through distraction and partly through fear, but she grows more decisive as the quest goes on. Her arc is about learning to trust instructions over her own comfort.
Eustace Scrubb
Eustace has already been to Narnia and been changed by it. He's more experienced than Jill but still makes mistakes, including missing the first sign at the dock. He functions as a guide who doesn't always know the way, which keeps the story from making him too reliable.
Puddleglum
The Marsh-wiggle is the adult of the group and the moral center of the story. He predicts failure constantly but never stops moving forward. His decision to stamp out the fire and reject the Lady's argument is the moment that saves everyone. Lewis uses him to show that pessimism and faithfulness can coexist.
The Lady of the Green Kirtle
The main villain. She works through enchantment, beauty, and false logic rather than direct force. She imprisoned Rilian, killed his mother in serpent form, and nearly convinces the travelers that reality itself is a lie. She dies as a serpent, which ties her to the original crime.
Prince Rilian
The lost prince has been under the Lady's spell for years. He only has one hour of clarity each night, and during that hour he's been told he's mad. When freed, he becomes capable and decisive. His story is about what happens to identity when someone else controls your perception of yourself.
Aslan
Aslan appears at the beginning to give Jill the signs and at the end to restore Caspian and scatter the bullies. He doesn't travel with the characters or rescue them directly. His role is to set the task and trust them to carry it out, which is what makes the signs so important.
King Caspian
Caspian appears briefly at the start as an old man on a ship and at the end dying in Narnia. His death and restoration frame the emotional stakes of the quest. Rilian's return gives Caspian a few moments with his son before he dies, and Aslan restores him to youth in his own country.