Dorothy is a bright and resourceful child who handles being transported into a new realm with resolve, good cheer, and an unwavering eagerness to return home. Though apparently younger than her companions (according to some readers' calculations, she is about 10 years old), she is as protective of them as they are of her. When confronted with evil (the Wicked Witch of the West) or with deception (Oz), Dorothy's strong sense of fairness upholds her.
Though the Scarecrow's dearest wish is that Oz give him a brain, he is already possessed of native intelligence. He learns quickly and usually comes up with a helpful idea when the travelers face a challenge.
The Woodman's goal is to obtain a heart from Oz. Yet he is already as sensitive and "tender-hearted" as if he had a real heart. He is brave and protective, but the sight of a friend or animal in trouble brings him to tears.
The Cowardly Lion isn't really the coward he believes himself to be. He proves himself brave and daring many times before Oz consents to provide him with courage.
Toto may be only a dog, but he sets the whole book in motion. He is devoted to Dorothy and clings to her side unless cats or other interesting objects cross his path. His instinctive curiosity has the effect of revealing truths that might not otherwise come to light.