Taran has several mentors throughout his journey—Dallben, Gwydion, and Medwyn. What do they each teach him about heroism?

Why does Eilonwy decides to rescue Taran from his dungeon cell? What does she teach him about heroism? In what way is she a foil to Taran, or a character who illuminates another character’s traits through contrasting qualities?

Eilonwy talks non-stop, and this annoys Taran. He, in turn, tries to insist on his own way without consulting her, and she finds that aggravating. How is each of their supposedly negative traits also virtues?