Wirt, the older brother, is rather self-absorbed and likes to keep to himself. He is quick to second guess his decisions and tends to see problems as unsolvable. This is mostly because he's afraid of making the wrong decision.
Greg, the younger brother, is energetic, playful and care-free...often to the point of being oblivious to serious danger. He loves life; only seeing the good and fun things around him...but he has trouble understanding that actions can have real consequences. Perhaps because of his innocence he is hardly afraid of anything.
Beatrice is a talking bluebird who comes to Wirt and Greg's aid to help them on their journey home. She says she can lead them to Adelaide of the Pasture, the Good Woman of the Woods, who in turn will help them get home.
It's hard to tell what makes the Woodsman tick. Is he dangerous? Is he helpful? Is he just a crazy guy who wanders around in the woods? In truth he is just another lost soul himself.
Greg always carries a frog around with him. The frog's name is constantly changing, and while Greg insists that the frog belongs to both himself and Wirt, he has zero interest in looking after the frog. The frog doesn't talk, but he does sing.